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  • JR-connector - 2X (3.5A each)
  • XT30-connector (30A)
  • Balance connector
Price: $34.99

    Quantity:
    Item #: B2S2500
    Availability: In stock
    Usually ships In the same business day

    This B2S2500 is a dedicated pack consisting of 2 LiIon cells arranged in a series configuration (two cells arranged side-by-side). Outputting well over 8V fresh off charge, this pack is intended for direct connection to receivers.

    Representing a lot of juice in a compact package, this pack is equipped with two JST (JR-type) connectors rated at 3.5A each (so combined they deliver 7A) along with an XT30 charge/discharge connector (rated at 30A). Plus, an HX-type balance connector for the charger (for monitoring SOC, or state of charge).

      • Type: 2S (two cells in series)
      • Capacity: 2500mAH
      • Nominal voltage: 7.4V
      • Full charge voltage: 8.4V
      • Charge rate: 1C (full charge in 60-minutes)
      • Continuous discharge rate: 20A
      • Burst discharge rate (5-sec): 30A
      • Weight: 107g (3.75oz)
      • Dimensions: 66 x 36 x 18 mm (2-5/8 x 1-3/4 x 3/4 inches).
      • Discharge connectors: JR-type (two)
      • Discharge connector: Amass XT30
      • Balance connector: JST XH-type

    Asked and answered over the years for various chemistries

    Q. At what rate should I charge my LiIon pack?

    A. In general, don't exceed 5C, and best practice is charge at 1C.

    Look, teaching you everything you need to know about battery charging is beyond the scope of this website. We'll share some examples to try and help guide you, but don't for a minute believe this is a comprehensive explanation. Point being, it's on you to learn enough to be safe and the charger manufacturer will also have information to use in safely charging your battery pack.

    To begin, you need to be aware of a bit of math. Like how the 'm' in mAh means mili, or 1/1000. Regarding the A, that means Amperes (or amps), and h=hours. So the capacity of the pack is measured amps delivered in one hour, or Ah (A*h or A x h), but since packs for models are often measured in fractions of an ampere, then they're also often expressed in terms of milliamps, or 1/1000th of amp. As for time, since the time frame is always based one hour, then . . .

    • 5000mAh = 5Ah - meaning it'll deliver 5A of current for one hour
    • 2000mAh = 2Ah
    • 850mAh = 0.85Ah

    . . . understand?

    Further to this, C (capacity) of a 5Ah pack is 5A for an hour, 2.5A for two hours. Similarly, 2A of consumption for an hour from a 2Ah pack, get it?

    So charging at 1C (meaning 1xC) it means a 5Ah pack can be charged at 5A, and if the same pack is being charged at 2C (meaning 2xC or 2x5=10) it means it can be charged at 10A and since we're dealing with full hours, this means it'll charge in 1/2 that much time, or 1/2 an hour. Confused? Continue reading.

    Let's switch to a 2Ah pack (same-same as a 2000mAh pack). Charging a fully discharged 2Ah pack at 1C means hitting it with the charger at 2A for one hour. Hit it at 2C (4A) means it takes half that much time (1h/2=1/2h or 30-minutes) Ditto, charging at 3C takes 1/3 of an hour or 20 minutes (60min/3=20minutes), or at 4C takes 1/4th of an hour, or 15 minutes. Get it? If not, review and consider learning about this material in other places until it clicks because if you screw up you're putting your life at risk.

    We're not kidding so please consider yourself warned!

    Note; all this is in theory because it's never a good idea to discharge below 20% capacity. Point being, a 5000mAh pack in practice should be considered 80% of 5ooomA (0.8 x 5000=4000), or 4000mAh instead of 5000mAh. This is important!

    There's more to learn, and it's not really rocket science, but it's on you to go learn about it before charging batteries. We're sharing some some rules of thumb that will for the most part keep you out of trouble - but - you can burn your house down by being stupid so don't go trying to blame us because a) we're telling you battery charging can be dangerous, and b) that what we're sharing isn't everything you need to know. The major point being, you should go learn how to do it safely before you begin!

    Q. My charger has a LiPo charge-cycle instead of LiIon. May I still use it?

    A. Yes.

    In general, chargers expressly made to charge LiIon packs are set to similar cell-voltages for LiPo-chemistry and thus, won't damage the pack. Basically, the difference internally is the LiIon cell has a liquid electrolyte while the LiPo, which is also a lithium-ion technology, uses a gel for the electrolyte. Anyway, always use a charger designed for the appropriate chemistry. Note; chargers are available to charge multiple chemistries.

    Q. My charger has a LiFe charge-cycle instead LiIon. May I still use it?

    A. In general, no for LiIon because a LiFe-charge cycle is going to charge at a lower level than for LiIon.

    Q. My battery is marked LiFePO4 instead of LiIon and marked 6.6V instead of 7.4V. My charger has a LiFe charge cycle, may I use this?

    A. Yes. Similar to how you can charge a LiIon with a LiPo charge cycle, LiFePO4 can be charged with a LiFe charge cycle. And like LiIon is similar to LiPo in chemistry and different in physical construction, LiFEPO4 is similar to LiFe with similar chemistry and different physical packaging (meaning LiFe are packaged in polymer bags like LiPo, and LiFePO4 within metal cylindrical cells like LiIon.

    And for our purposes (handling and use within models), for pretty much the same reason; meaning they're more robust and thus, more readily withstand the knocks of life better. Like what? Shifting within the fuselage during a crankshaft maneuver, maybe and if it's a soft side construction, maybe bumping up against he hard edge of a plywood or carbon fiber former, and getting a ding.

    What's important about this is even if you smooth the ding over with the ball of your thumb until you can't see it, the ding damaged the electrolyte. Forevermore, there's a damaged place (maybe now invisible to the eye) but where heat can build up during charge and discharge.Honestly? This could mean a fire in your workshop or home. Heads up!

    Q. I've been told LiIon are safer than LiPo and I don't have to worry about discharging them and storing in fireproof bags. is this true?

    A. There's safer and then there's SAFER. While somewhat less prone to spontaneously fire than LiPo battery packs, LiIon packs can and do catch fire. What may lead to this happening? I'm not a battery designer or chemist, in this instance this is me, John, trying to help guide you like I was taught by those who knew more than me. So I'm sharing my experience and trying to help you learn a few of the things I have learned. Point being, you need to do some research on your own to confirm pretty much anything and everything you learn, not just here, but elsewhere. So here's what I know.

    Look, chargers can malfunction and never stop charging. This, maybe leading packs to overheat and catch fire. We see example of LiIon fires in popular press stories like this one in the NY Post:

    Major point being, electric scooters and bikes also use these cylindrical cells (maybe because they fit nicely inside round steel tube frames), so if I were you, I'd be careful about trusting *any* battery pack. Me? I store them in fireproof bags of the type you can buy pretty much anywhere (I buy mine off Amazon). Even then, I store these batteries inside a .50 caliber ammo can, which I bought at an Army surplus store. Note; I drilled a 1/4" hole in the lid (because they seal, otherwise). This, so if one catches fire it can vent the pressure. Next, I epoxied a bit of stainless steel wool wool on the underside (and over the hole - but - careful not to plug it with epoxy). The purpose of this is to serve as a smoke trap and maybe minimize the mess. Does it work? Dunno, never had a fire. Just relating what *I* do . . . but you do you, as the saying goes.

    Q. Do I need to put my LiFePO4 battery packs at storage mode like I do my LiPo propulsion-packs and my LiIon receiver-packs?

    A. No, it's our experience these are the only packs you will own where it doesn't seem to hurt them to charge today and go fly tomorrow, or next week, or in six-months! Like if your better-half has other ideas and the next day while you're loading the truck with models she announces, 'It's almost spring, take me shopping for painted Mexican terracotta pots, honey!' This, being an example of the now classic, honey-do! So you being a long suffering fellow happily married man, and well experienced in the ways of women, say, 'But of course, Dear, when do you have in mind we should go?"

    Saying unlike a LiIon or LiPo which you should soon after deciding you're not going flying connect to your charger and run a storage mode cycle, with the LiFePO4 packs I've found you can ignore and use them when you're good and ready.

    Q. I saw a datasheet for a LiFePO4 cell and it refers to them as LiIon, what's going on with that?

    A. Technically, all cylindrical cell batteries are LiIon. It's just that there are different types so just like there are Lithium-Iron-Phosphate (LiFePO4 or more commonly in the industry, LFP), there are Lithium-Manganese-Oxide (LMO), Lithium Nickle Manganese Cobalt Oxide (NMC), Lithium-Nickle-Cobalt-Aluminum-Oxide (NCA), Lithium-Cobalt-Oxide (LCO) and Lithium-Titanium-Oxide (LTO), and soon enough, others. And the one thing they share is a different balance of;

    • Cost
    • Life Span
    • Specific Energy
    • Performance
    • Specific Power
    • Safety

    The best one for Specific Power, Safety, and Life Span is the LFP. And because these use materials that are comparatively dirt cheap (iron and phosphate instead of nickel and cobalt), they're less costly. And good and cheap is often a winning combination in many things, same with batteries in my opinion. The downside is their Performance and Specific Energy, so LFP cells have less voltage than other types, 3.2-3.3 versus 3.7-3.8 and this makes them safer and less prone to spontaneously catching fire.These are good things i my view, what about yours?

    But less voltage isn't as desirable as higher voltage because servos make more torque and operate faster on higher voltage (not just ProModeler, all servos, all brands - due to physics, not marketing) so a caution you should bear in mind is since servos are marketed by applying lipstick to the pig (again, all servos, not just ours), they're rated on 8.4V instead of 6.6V because that's where they shine!

    Major point being, if you need 350oz-in and you figure you're good because you're buying our DS360DLHV servos, think again if you're planning on running them on a LFP pack because on 6.6V, they won't make 350oz-in. We're very careful to disclose more than just 6.0V and 8.4V specs and this is a perfect example of why. The DS360 is rate at 8.4V and it gives you 360oz-in but at 6.6V it's down to 290oz-in. Maybe good enough, maybe not. Judgement call.

    But . . .

    . . . if you look instead at the specs chart for the DS415BLHV servo (rated at 8.4V, remember), then at 6.6V it's still making 345oz-in and that's a *lot* closer to the 350oz-in you want. But, for another ten bucks, you can, also . . .

    . . . check out the DS505BLHV servo, which at 6.6V it's still making a whopping 450oz-in. Me? I like a bit of overkill, what about you?

    So the take away from this is give consideration to your servos when selecting your battery chemistry. Word to the wise.

    Q. Can I charge my 2S LiIon pack with a NiCd charger for 7-cells since that's designed to charge 7.2V packs?

    A. Not just no . . . but Hell no! And not just don't do it . . . don't even *think* about it.

    The reason is the NiCd charger makes no provision to monitor the cell voltage of the individual cells the way a charger designed for LiIon packs will. This is the inherent advantage of the LiIon technology in that each cell is wired to the little white balance-connector so the charger can monitor the voltage of each cell as it charges. Be careful because this is a good way to start a fire and burn down your house! You've been warned!

    Q. I've heard if I run a LiIon or LFP pack down too low for the charger to start the cycle, you can unplug the balance connector and set it NiCd-type in the program and it'll start right up and get some juice into the pack - enough to start the cycle with the balance connector connected.

    A. This is true. And if you do it out on the concrete of your driveway (where if it catches fire there's less risk - but remember, you have to explain it to the fire department and the insurance company adjuster if things go teats up), then maybe you can get away with it. Perhaps 5-10-min, where the charger is set to charge a 7-cell NiCd pack (because 7x1.2V/cell equals about the same as an 8.4V 2S LiIon, or as a 7.2V 6-cell NiCd, again where 6x1.2V/cell mimic a 2S LFP), maybe you can get enough current into the pack to bring the voltage up enough for the automated charge cycle to take over.
    So yes, I know this may work . .. but riddle me this. What's a model worth to you, a few hundred bucks, maybe even several thousand? And what will you say during a deposition when opposing counsel asks, 'Sir, why would you try to save $30 resuscitating a battery, didn't you realize it could die unexpectedly, only to lose control and fly through the windshield of you buddy's parked car where his wife was crocheting booties for their granddaughter, and kill her?

    Just saying, there's being smart by saving a few bucks, and then being really smart and realizing when to cut your loses. Like maybe this is one of those times when it's smarter to take the battery pack to be recycled. Just saying, I wouldn't *but* you do you because to your question, yes, folks have done this successfully.

    Q. I'm Canadian and fly year around, sometimes in sub-zero temperatures. Is it OK to charge my LiIon pack in these conditions?

    A. Yes, but be careful. Capacity is reduced maybe 20-30% at freezing. And at lower temperatures the data is inconsistent. Look, batteries basically like to 'live' at similar temperatures where 'we' like to live. Fortunately, in practice, what most folks do is charge their packs whilst in their car!

    That said, if you do charge in below freezing temperatures, reduce the rate of charge to 0.1C . . . e.g. 10% of the battery capacity.

    Q. I'm confused, isn't LiIon the same as LiPo? Also, why don't you recommend LiPo packs? I like that they're cheap so what's wrong with that?

    A. Yes, LiIon and LiPo are similar. But critical differences aren't so much in their chemistry (they're actually very similar) but in their methods of construction. This is the key to understanding our recommendation for LiIon versus LiPo.

    This is because the LiPo is built in a polymer bag. This gives it the characteristic brick shape as the individual cells are flat-rectangles, which are overlaid upon one another. The shape is also the giveaway for the LiPo vs. LiIon where these packs are built within cylindrical metal shells (typically aluminum).

    Note; the Po in LiPo refers to the polymer in it's construction (aluminized polymer bags). Anyway, the individual cylindrical shells, because they're made of metal instead of thin polymer bags means they're more resistant to physical damage. By the way, this metal shell is the same technology used in old school NiCds and NiMH (and alkaline cells, for that matter). It's been around forever because it works!

    There are downsides to these metal shells. First, the metal is a bit heavier than the plastic bag use in LiPos. Second, simple geometry dictates two cylinders contain less volume than two flat cells (capacity). Third, they're more expensive to produce.

    Against these disadvantages are upsides. Like metal shell is FAR more sturdy. This turns out to be a crucial advantage because metal protects better against inadvertent damage (like a pack shifting during a maneuver and bumping up against the hard edge of a former). If this happens to polymer style packs, the dent may result in it puffing. Or in a fire. Need I mention our models are constructed of flammable materials like balsa, foam, and fiberglass?

    Bottom line? For an engineer, part of the remit is looking not at when everything is going right, but when things are going wrong. Look, nobody sets out to install their pack so it's dented due to shifting during a maneuver, but . . . shit happens, right? So it's when things go pear shape that a good engineer earns his pay.

    Our deciding against continuing to offer 'Po' style packs for control avionics is a direct result of data indicating it might sound good in theory, but in practice, leaves something to be desired. This reminds of the immortal words of a wise wag of baseball.

    Put another way, when the data changes, we change our mind! This is why our control avionic pack recommendation is to use durable LiIon instead of more fragile and less costly alternatives like LiPo brick style packs.

    Q. How did you come to make batteries with two leads?

    A. I've mentioned how and why. before . . . now for the rest of the story.

    Way back in the day, going back on the order of 50 years ago, I flew a Lou Andrews Aeromaster (53" wingspan). Loved that model flew it for many years. Re-covered it twice - thank goodness for K2R spray. Powered by my Lee Custom K&B .61 on SIG 5% with 2% added castor and turning a 12x6, it was a delightful model until it met an untimely demise due to switch failure. This crash led me to develop a two-lead battery pack.

    This all aided by Mr. Kraft of Kraft Systems who generously agreed to sell me 25 of their 4-cell NiCd 500mAh battery packs, to include 25 extra leads (no other source for a Multicon connector since that was their proprietary product), and he even included a sheet of gold foil labels with which to reseal the case halves like brand new for after I soldered on the 2nd lead. I was on my own for finding a larger rubber grommet but he even lent me a hand with this by including a small bag of servo mounting grommets. And he gave me some round Kraft patches to hand out, too.

    All this in part because (and I am reading into his actions what I *think* were the reasons). Meaning, I think he, a) didn't want to complicate his life with another SKU (stock keeping unit in the parlance of product sales), and b) believed his switches were reliable enough, and looking back, c) it maybe tickled him to help start someone (me) get a start in a business career.

    Me? I will remain forever grateful to his largess to a snot nose kid with a business idea because he could have blown me off. Unfortunately, when I went off to college, my mom wanted the room for whatever and tossed pretty everything that remained of my life there. By this meaning my paperback science fiction books (I've subsequently replaced my Heinlein, Clark,and Asimov and added to them the rest in print (except Asimov as I don't have that much money). She also tossed things like my sandpaper collection stored within an accordion file my grandfather had given me (embossed with his law office logo, and of course, irreplaceable), plus my correspondence with Mr. Kraft, which at the time i didn't attach much importance to. So basically, pretty much everything I hadn't taken with me to university - to include my modeling tools - like sanding blocks, X-Acto, Zona saw, model razor plane, workbench, etc. went into the ash bin as she basically erased me like I was never there. And looking back, this sounds bad but she wanted the room and all my stuff looked like just trash to her broom!

    Sounds worse than it is, but within a few years I was married and making my own life anyway. Anyway, my gratitude to Mr. Kraft knows no bounds for providing me air cover (so to speak) for my ground assault (I was selling these 2-lead batteries to my mates in the club and soon enough to folks in two other clubs). This was my first business venture (if you don't count lawn mowing and delivering morning edition newspapers for the Birmingham News on my bike). Today? Mr Kraft long ago flew west, his business is mothballed, and me? Multi-lead batteries are still in our product lineup.

    Now, unlike then, two benefits accrue of having packs with multiple leads. The first being you can use 2 on/off switches (my principal purpose way back when). This, because it affords inexpensive redundancy. After all, odds of both radio switches failing on the same flight are astronomical.

    The other benefit of two leads? Not a big deal back when servos only drew a few hundred milliamps, but a really big deal, today when individual servos easily draw several amps (1A=1000mA). Since each battery lead is rated at 3.5A, then making two connections to the receiver through individual leads benefits you in making 7A of current available instead of 3.5A (before heat build up since this is a rating, not a limit). And this is a bigger deal than most modelers realize.

    Note; for propulsion, the weight and package volume (capacity) give an overwhelming advantage to polymer bag construction. This is why LiPo packs are used for powering RC models. But also know this, these packs are removed prior to charging (or should be), so the risk profile is somewhat different.

    Q. At what rate should I charge my LiIon pack?

    A. In general, don't exceed 5C, and best practice is charge at 1C.

    Look, teaching you everything you need to know about battery charging is beyond the scope of this website. We'll share some examples to try and help guide you, but don't for a minute believe this is a comprehensive explanation. Point being, it's on you to learn enough to be safe and the charger manufacturer will also have information to use in safely charging your battery pack.

    To begin, you need to be aware of a bit of math. Like how the 'm' in mAh means mili, or 1/1000. Regarding the A, that means Amperes (or amps), and h=hours. So the capacity of the pack is measured amps delivered in one hour, or Ah (A*h or A x h), but since packs for models are often measured in fractions of an ampere, then they're also often expressed in terms of milliamps, or 1/1000th of amp. As for time, since the time frame is always based one hour, then . . .

    • 5000mAh = 5Ah - meaning it'll deliver 5A of current for one hour
    • 2000mAh = 2Ah
    • 850mAh = 0.85Ah

    . . . understand?

    Further to this, C (capacity) of a 5Ah pack is 5A for an hour, 2.5A for two hours. Similarly, 2A of consumption for an hour from a 2Ah pack, get it?

    So charging at 1C (meaning 1xC) it means a 5Ah pack can be charged at 5A, and if the same pack is being charged at 2C (meaning 2xC or 2x5=10) it means it can be charged at 10A and since we're dealing with full hours, this means it'll charge in 1/2 that much time, or 1/2 an hour. Confused? Continue reading.

    Let's switch to a 2Ah pack (same-same as a 2000mAh pack). Charging a fully discharged 2Ah pack at 1C means hitting it with the charger at 2A for one hour. Hit it at 2C (4A) means it takes half that much time (1h/2=1/2h or 30-minutes) Ditto, charging at 3C takes 1/3 of an hour or 20 minutes (60min/3=20minutes), or at 4C takes 1/4th of an hour, or 15 minutes. Get it? If not, review and consider learning about this material in other places until it clicks because if you screw up you're putting your life at risk.

    We're not kidding so please consider yourself warned!

    Note; all this is in theory because it's never a good idea to discharge below 20% capacity. Point being, a 5000mAh pack in practice should be considered 80% of 5ooomA (0.8 x 5000=4000), or 4000mAh instead of 5000mAh. This is important!

    There's more to learn, and it's not really rocket science, but it's on you to go learn about it before charging batteries. We're sharing some some rules of thumb that will for the most part keep you out of trouble - but - you can burn your house down by being stupid so don't go trying to blame us because a) we're telling you battery charging can be dangerous, and b) that what we're sharing isn't everything you need to know. The major point being, you should go learn how to do it safely before you begin!

    Q. My charger has a LiPo charge-cycle instead of LiIon. May I still use it?

    A. Yes.

    In general, chargers expressly made to charge LiIon packs are set to similar cell-voltages for LiPo-chemistry and thus, won't damage the pack. Basically, the difference internally is the LiIon cell has a liquid electrolyte while the LiPo, which is also a lithium-ion technology, uses a gel for the electrolyte. Anyway, always use a charger designed for the appropriate chemistry. Note; chargers are available to charge multiple chemistries.

    Q. My charger has a LiFe charge-cycle instead LiIon. May I still use it?

    A. In general, no for LiIon because a LiFe-charge cycle is going to charge at a lower level than for LiIon.

    Q. My battery is marked LiFePO4 instead of LiIon and marked 6.6V instead of 7.4V. My charger has a LiFe charge cycle, may I use this?

    A. Yes. Similar to how you can charge a LiIon with a LiPo charge cycle, LiFePO4 can be charged with a LiFe charge cycle. And like LiIon is similar to LiPo in chemistry and different in physical construction, LiFEPO4 is similar to LiFe with similar chemistry and different physical packaging (meaning LiFe are packaged in polymer bags like LiPo, and LiFePO4 within metal cylindrical cells like LiIon.

    And for our purposes (handling and use within models), for pretty much the same reason; meaning they're more robust and thus, more readily withstand the knocks of life better. Like what? Shifting within the fuselage during a crankshaft maneuver, maybe and if it's a soft side construction, maybe bumping up against he hard edge of a plywood or carbon fiber former, and getting a ding.

    What's important about this is even if you smooth the ding over with the ball of your thumb until you can't see it, the ding damaged the electrolyte. Forevermore, there's a damaged place (maybe now invisible to the eye) but where heat can build up during charge and discharge.Honestly? This could mean a fire in your workshop or home. Heads up!

    Q. I've been told LiIon are safer than LiPo and I don't have to worry about discharging them and storing in fireproof bags. is this true?

    A. There's safer and then there's SAFER. While somewhat less prone to spontaneously fire than LiPo battery packs, LiIon packs can and do catch fire. What may lead to this happening? I'm not a battery designer or chemist, in this instance this is me, John, trying to help guide you like I was taught by those who knew more than me. So I'm sharing my experience and trying to help you learn a few of the things I have learned. Point being, you need to do some research on your own to confirm pretty much anything and everything you learn, not just here, but elsewhere. So here's what I know.

    Look, chargers can malfunction and never stop charging. This, maybe leading packs to overheat and catch fire. We see example of LiIon fires in popular press stories like this one in the NY Post:

    Major point being, electric scooters and bikes also use these cylindrical cells (maybe because they fit nicely inside round steel tube frames), so if I were you, I'd be careful about trusting *any* battery pack. Me? I store them in fireproof bags of the type you can buy pretty much anywhere (I buy mine off Amazon). Even then, I store these batteries inside a .50 caliber ammo can, which I bought at an Army surplus store. Note; I drilled a 1/4" hole in the lid (because they seal, otherwise). This, so if one catches fire it can vent the pressure. Next, I epoxied a bit of stainless steel wool wool on the underside (and over the hole - but - careful not to plug it with epoxy). The purpose of this is to serve as a smoke trap and maybe minimize the mess. Does it work? Dunno, never had a fire. Just relating what *I* do . . . but you do you, as the saying goes.

    Q. Do I need to put my LiFePO4 battery packs at storage mode like I do my LiPo propulsion-packs and my LiIon receiver-packs?

    A. No, it's our experience these are the only packs you will own where it doesn't seem to hurt them to charge today and go fly tomorrow, or next week, or in six-months! Like if your better-half has other ideas and the next day while you're loading the truck with models she announces, 'It's almost spring, take me shopping for painted Mexican terracotta pots, honey!' This, being an example of the now classic, honey-do! So you being a long suffering fellow happily married man, and well experienced in the ways of women, say, 'But of course, Dear, when do you have in mind we should go?"

    Saying unlike a LiIon or LiPo which you should soon after deciding you're not going flying connect to your charger and run a storage mode cycle, with the LiFePO4 packs I've found you can ignore and use them when you're good and ready.

    Q. I saw a datasheet for a LiFePO4 cell and it refers to them as LiIon, what's going on with that?

    A. Technically, all cylindrical cell batteries are LiIon. It's just that there are different types so just like there are Lithium-Iron-Phosphate (LiFePO4 or more commonly in the industry, LFP), there are Lithium-Manganese-Oxide (LMO), Lithium Nickle Manganese Cobalt Oxide (NMC), Lithium-Nickle-Cobalt-Aluminum-Oxide (NCA), Lithium-Cobalt-Oxide (LCO) and Lithium-Titanium-Oxide (LTO), and soon enough, others. And the one thing they share is a different balance of;

    • Cost
    • Life Span
    • Specific Energy
    • Performance
    • Specific Power
    • Safety

    The best one for Specific Power, Safety, and Life Span is the LFP. And because these use materials that are comparatively dirt cheap (iron and phosphate instead of nickel and cobalt), they're less costly. And good and cheap is often a winning combination in many things, same with batteries in my opinion. The downside is their Performance and Specific Energy, so LFP cells have less voltage than other types, 3.2-3.3 versus 3.7-3.8 and this makes them safer and less prone to spontaneously catching fire.These are good things i my view, what about yours?

    But less voltage isn't as desirable as higher voltage because servos make more torque and operate faster on higher voltage (not just ProModeler, all servos, all brands - due to physics, not marketing) so a caution you should bear in mind is since servos are marketed by applying lipstick to the pig (again, all servos, not just ours), they're rated on 8.4V instead of 6.6V because that's where they shine!

    Major point being, if you need 350oz-in and you figure you're good because you're buying our DS360DLHV servos, think again if you're planning on running them on a LFP pack because on 6.6V, they won't make 350oz-in. We're very careful to disclose more than just 6.0V and 8.4V specs and this is a perfect example of why. The DS360 is rate at 8.4V and it gives you 360oz-in but at 6.6V it's down to 290oz-in. Maybe good enough, maybe not. Judgement call.

    But . . .

    . . . if you look instead at the specs chart for the DS415BLHV servo (rated at 8.4V, remember), then at 6.6V it's still making 345oz-in and that's a *lot* closer to the 350oz-in you want. But, for another ten bucks, you can, also . . .

    . . . check out the DS505BLHV servo, which at 6.6V it's still making a whopping 450oz-in. Me? I like a bit of overkill, what about you?

    So the take away from this is give consideration to your servos when selecting your battery chemistry. Word to the wise.

    Q. Can I charge my 2S LiIon pack with a NiCd charger for 7-cells since that's designed to charge 7.2V packs?

    A. Not just no . . . but Hell no! And not just don't do it . . . don't even *think* about it.

    The reason is the NiCd charger makes no provision to monitor the cell voltage of the individual cells the way a charger designed for LiIon packs will. This is the inherent advantage of the LiIon technology in that each cell is wired to the little white balance-connector so the charger can monitor the voltage of each cell as it charges. Be careful because this is a good way to start a fire and burn down your house! You've been warned!

    Q. I've heard if I run a LiIon or LFP pack down too low for the charger to start the cycle, you can unplug the balance connector and set it NiCd-type in the program and it'll start right up and get some juice into the pack - enough to start the cycle with the balance connector connected.

    A. This is true. And if you do it out on the concrete of your driveway (where if it catches fire there's less risk - but remember, you have to explain it to the fire department and the insurance company adjuster if things go teats up), then maybe you can get away with it. Perhaps 5-10-min, where the charger is set to charge a 7-cell NiCd pack (because 7x1.2V/cell equals about the same as an 8.4V 2S LiIon, or as a 7.2V 6-cell NiCd, again where 6x1.2V/cell mimic a 2S LFP), maybe you can get enough current into the pack to bring the voltage up enough for the automated charge cycle to take over.
    So yes, I know this may work . ..  but riddle me this. What's a model worth to you, a few hundred bucks, maybe even several thousand? And what will you say during a deposition when opposing counsel asks, 'Sir, why would you try to save $30 resuscitating a battery, didn't you realize it could die unexpectedly, only to lose control and fly through the windshield of you buddy's parked car where his wife was crocheting booties for their granddaughter, and kill her?

    Just saying, there's being smart by saving a few bucks, and then being really smart and realizing when to cut your loses. Like maybe this is one of those times when it's smarter to take the battery pack to be recycled. Just saying, I wouldn't *but* you do you because to your question, yes, folks have done this successfully.

    Q. I'm Canadian and fly year around, sometimes in sub-zero temperatures. Is it OK to charge my LiIon pack in these conditions?

    A. Yes, but be careful. Capacity is reduced maybe 20-30% at freezing. And at lower temperatures the data is inconsistent. Look, batteries basically like to 'live' at similar temperatures where 'we' like to live. Fortunately, in practice, what most folks do is charge their packs whilst in their car!

    That said, if you do charge in below freezing temperatures, reduce the rate of charge to 0.1C . . . e.g. 10% of the battery capacity.

    Q. I'm confused, isn't LiIon the same as LiPo? Also, why don't you recommend LiPo packs? I like that they're cheap so what's wrong with that?

    A. Yes, LiIon and LiPo are similar. But critical differences aren't so much in their chemistry (they're actually very similar) but in their methods of construction. This is the key to understanding our recommendation for LiIon versus LiPo.

    This is because the LiPo is built in a polymer bag. This gives it the characteristic brick shape as the individual cells are flat-rectangles, which are overlaid upon one another. The shape is also the giveaway for the LiPo vs. LiIon where these packs are built within cylindrical metal shells (typically aluminum).

    Note; the Po in LiPo refers to the polymer in it's construction (aluminized polymer bags). Anyway, the individual cylindrical shells, because they're made of metal instead of thin polymer bags means they're more resistant to physical damage. By the way, this metal shell is the same technology used in old school NiCds and NiMH (and alkaline cells, for that matter). It's been around forever because it works!

    There are downsides to these metal shells. First, the metal is a bit heavier than the plastic bag use in LiPos. Second, simple geometry dictates two cylinders contain less volume than two flat cells (capacity). Third, they're more expensive to produce.

    Against these disadvantages are upsides. Like metal shell is FAR more sturdy. This turns out to be a crucial advantage because metal protects better against inadvertent damage (like a pack shifting during a maneuver and bumping up against the hard edge of a former). If this happens to polymer style packs, the dent may result in it puffing. Or in a fire. Need I mention our models are constructed of flammable materials like balsa, foam, and fiberglass?

    Bottom line? For an engineer, part of the remit is looking not at when everything is going right, but when things are going wrong. Look, nobody sets out to install their pack so it's dented due to shifting during a maneuver, but . . . shit happens, right? So it's when things go pear shape that a good engineer earns his pay.

    Our deciding against continuing to offer 'Po' style packs for control avionics is a direct result of data indicating it might sound good in theory, but in practice, leaves something to be desired. This reminds of the immortal words of a wise wag of baseball.

    Put another way, when the data changes, we change our mind! This is why our control avionic pack recommendation is to use durable LiIon instead of more fragile and less costly alternatives like LiPo brick style packs.

    Q. How did you come to make batteries with two leads?

    A. I've mentioned how and why. before . . . now for the rest of the story.

    Way back in the day, going back on the order of 50 years ago, I flew a Lou Andrews Aeromaster (53" wingspan). Loved that model flew it for many years. Re-covered it twice - thank goodness for K2R spray. Powered by my Lee Custom K&B .61 on SIG 5% with 2% added castor and turning a 12x6, it was a delightful model until it met an untimely demise due to switch failure. This crash led me to develop a two-lead battery pack.

    This all aided by Mr. Kraft of Kraft Systems who generously agreed to sell me 25 of their 4-cell NiCd 500mAh battery packs, to include 25 extra leads (no other source for a Multicon connector since that was their proprietary product), and he even included a sheet of gold foil labels with which to reseal the case halves like brand new for after I soldered on the 2nd lead. I was on my own for finding a larger rubber grommet but he even lent me a hand with this by including a small bag of servo mounting grommets. And he gave me some round Kraft patches to hand out, too.

    All this in part because (and I am reading into his actions what I *think* were the reasons). Meaning, I think he, a) didn't want to complicate his life with another SKU (stock keeping unit in the parlance of product sales), and b) believed his switches were reliable enough, and looking back, c) it maybe tickled him to help start someone (me) get a start in a business career.

    Me? I will remain forever grateful to his largess to a snot nose kid with a business idea because he could have blown me off. Unfortunately, when I went off to college, my mom wanted the room for whatever and tossed pretty everything that remained of my life there. By this meaning my paperback science fiction books (I've subsequently replaced my Heinlein, Clark,and Asimov and added to them the rest in print (except Asimov as I don't have that much money). She also tossed things like my sandpaper collection stored within an accordion file my grandfather had given me (embossed with his law office logo, and of course, irreplaceable), plus my correspondence with Mr. Kraft, which at the time i didn't attach much importance to. So basically, pretty much everything I hadn't taken with me to university - to include my modeling tools - like sanding blocks, X-Acto, Zona saw, model razor plane, workbench, etc. went into the ash bin as she basically erased me like I was never there. And looking back, this sounds bad but she wanted the room and all my stuff looked like just trash to her broom!

    Sounds worse than it is, but within a few years I was married and making my own life anyway. Anyway, my gratitude to Mr. Kraft knows no bounds for providing me air cover (so to speak) for my ground assault (I was selling these 2-lead batteries to my mates in the club and soon enough to folks in two other clubs). This was my first business venture (if you don't count lawn mowing and delivering morning edition newspapers for the Birmingham News on my bike). Today? Mr Kraft long ago flew west, his business is mothballed, and me? Multi-lead batteries are still in our product lineup.

    Now, unlike then, two benefits accrue of having packs with multiple leads. The first being you can use 2 on/off switches (my principal purpose way back when). This, because it affords inexpensive redundancy. After all, odds of both radio switches failing on the same flight are astronomical.

    The other benefit of two leads? Not a big deal back when servos only drew a few hundred milliamps, but a really big deal, today when individual servos easily draw several amps (1A=1000mA). Since each battery lead is rated at 3.5A, then making two connections to the receiver through individual leads benefits you in making 7A of current available instead of 3.5A (before heat build up since this is a rating, not a limit). And this is a bigger deal than most modelers realize.

    Note; for propulsion, the weight and package volume (capacity) give an overwhelming advantage to polymer bag construction. This is why LiPo packs are used for powering RC models. But also know this, these packs are removed prior to charging (or should be), so the risk profile is somewhat different.