Lithium-Polymer Batteries — Part 1

Airsoft is a world full of old technology and an industry of slow moving innovation.  Look at the batteries we use.  Up until recenlty, most AEG’s came with nothing more than a NiCad battery, and most only with an 8.4v.  The discharge rate of the cells were poor, and you had to deal with poor quality Tamiya connectors, as well as thin and low quality wiring.  It’s time to update the technology we use.

Let us address some myths regarding lipos:

  1. Lipos WILL explode and are very dangerous to use
  2. Lipos are too powerful for anything but a heavily upgraded airsoft gun.
  3. Lipos require a lot of babying

Number One

Okay, so the first one isn’t really a myth, but hearing the horror stories some people tell, you’d think that lipos are prone to failure and then spawn gremlins who then tear up your garden, embroider your underwear, wet your bed, then swap your sports car with a Prius.  Yes, lipos CAN (not will) explode if you push them out of spec.  The same can be said about NiCad and NiMH batteries too!  Granted, the later two don’t often fireball, they can spit out all kinds of nasties that will burn you and possibly catch fire in addition to spewing shrapnel upon failure.  Keep your lipo within specs (easy to do), and you’ll nary have a problem!

Number Two

Number two has to be one of the most annoying things I hear about lipos.  Everyone is afraid of the big bad lipo battery!  Why do people think that a lipo will blow up your AEG?  I just don’t get it.  Let’s learn some math and understand why this is total nonsense!

First we must understand a thing called discharge rate.  This is the rate at which current flows out of the battery.  Manufacturers refer to this as the “C” rate of the battery.  So if your battery specs say that you have an 11.1v 2200mAh 25C battery, then you know the discharge rate is 25C.  Now what does that mean?  Well, let’s convert that to something we can understand.  To convert the “C” rate to amps (a measure of current), we just use this formula:

C Rate x Capacity (in amp hours) = Discharge Rate in Amps

So let’s look back at the battery we were just talking about.  Using the formula we have 25C x 2.2Ah = 55A.  Now hold up a minute and don’t freak out when you see that 55A rating.  We’ll get to that in just a second.  What you need to know is that 55amps is what that battery is CAPABLE of producing.  Now let’s switch gears and see what that NiMH battery you have is capable of producing.  Most NiMH cells used in Airsoft can discharge with a C rate of up to 12C.  Hum…. see where I’m going don’t you?  Keep reading.  So let’s look at an average mini battery that might come with an AEG; say a 8.4v 1400mAh NiMH battery.  Using the formula above we find that it is capable of discharging 16.8amps continuously.  Wow, big difference.

Okay, enough of the math, what does that mean to you and your AEG?  Every AEG needs a certain amount of current to run.  This can vary from setup to setup due to different requirements of the motor and the load it has to drive as determined by the spring strength and gear ratios.  Let us look at my M249 for an example.  Drivetrain-wise, here are the specs:

  • Guarder High Speed Motor
  • Madbull M120 Spring
  • Standard Ratio Gears
  • 8mm Bearings

Now this gun requires about 22A to drive it, and since it’s a PARA version, it only houses a mini battery.  WAIT!  Didn’t we just find out that the mini battery in the above example only can put out up to 16.8 amps!?!?!?  That’s under powering the gun by about 23.6%! So what can we do to increase the performance given the tiny space we have to fit a battery?  Well, we can put the battery someplace else and use a larger battery, but that might not be an option.  Then we can increase the voltage from 8.4v to 9.6v.  Well in this case, there is room to add the extra cell.  Adding more voltage will increase the ROF and provide more power to the system but you might not have room for the extra cell either; there must be a better way.  Enter Lithium-Polymer batteries; stage right.  Lipo batteries are able to fit higher capacities and higher discharge rates into smaller packages than a traditional NiMH or NiCad battery.  So let us revisit our space and current conundrum.

We need 22 amps of current to drive our system (AEG’s drivetrain) at 100%.  So let us use a 7.4v 2200mAh 25C lipo battery.  That has a discharge rate of 55A.  Of course, the gun only needs 22A…. and as such WILL ONLY DRAW 22A.  The gun can’t and will not use more current than it needs.  It will however, try to pull as much as it needs.  So when you’re putting that mini battery we talked about earlier in there, we’re over taxing the motor and the battery as the motor tries to draw the full 22A out of something that can’t supply it.  With the lipo, we have only used 40% of it’s capability; thus not overtaxing any part of the system!  Did you also notice we’re only using 7.4v to drive the system?  Nice huh?

So let’s get back to myth number two that says we have to have a heavily upgraded gun to run a lipo.  If you were to run a stock gun at 100%, and the stock internals are capable of handling the gun running at 100%, then using a lipo is no problem.  Where you run into problems is systems that arn’t matched.  You might have a heavy spring with a motor that can’t provide enough torque.  Or maybe you have a low quality piston or gears in a high fps rig.  Then you’re system isn’t matched (strength of the drivetrain to the load being driven), and regardless of what type of battery your run (3300mAh NiMH or a 2200mAh Lipo 25C), you’re just as likely to trash the piston or gears.  DON’T BLAME THE LIPO!

We’ll get to myth 3 soon enough, but I want to give you a moment to chew on all of this information.  Let’s see what we’ve learned.

First, as long as lipos are kept within the manufacturers specifications, they’ll run reliably for a long time.  Just like NiMH or NiCad’s they’ll present you with a potential fireball of a hazard if you push them outside of the manufacturer specs.

Second, it’s not the lipo that can kill your gun, it’s unmatched components being driving at 100%.  If the motor is running at 100%, but the gears are operating at 140% of their ability because of poor quality, then they’ll break. Same is true of the piston and anything else in the gearbox.  With that line of thought, a 7.4v lipo is no more likely to break your gun than a large 9.6v NiMH or NiCad!

Well, chew on that for a while and we’ll get to myth three in the next part when we discuss maintaining, charging, storage and precautions for your lipo battery.

Part 2

18 responses

20 08 2008

Great article. I’ve been using LiPo’s in my airsoft guns for over a year now, both upgraded and stock, with nothing but great results.

11 07 2009

great article it really opened my eyes to alot about lipos that i didnt know.

2 09 2009
LIPO batteries?

[...] [...]

26 05 2010
Lipo Info thread

[...] Date: Jan 2010Location: Millville, NJPosts: 101 I found this read extremely useful. Lithium-Polymer Batteries — Part 1  Newbs90View Public ProfileSend a private message to Newbs90Find More Posts by Newbs90 Donate [...]

22 06 2010
Lipoly vs Nimh

[...] to first when asking about lipo batteries. And like I always say you should probably read it twice. Lithium-Polymer Batteries — Part 1 __________________FREE Airsoft Gear  blacksheepView Public [...]

12 09 2011

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10 10 2011
Mike Watkins

Just as a point about DC motors and current demand. You state, “The gun can’t and will not use more current than it needs. It will however, try to pull as much as it needs.” This statement is true on the surface but can be misleading. The current that a DC motor will draw is based on two factors, internal resistance and the Voltage applied. That determines the current draw. The internal resistance remains the same at any voltage. Upping the Voltage applied also increases the current demand. If the ICS Turbo 3000 dc motor rated for 102 Watts has an internal resistance of .7 Ohms, at 8.4 volts, the current will be 12.1 amps. At 11.1 Volts, the current demand will be 15.99 amps. So you are correct that a motor will demand a certain amount of current, but that in turn is dependent on the voltage applied. (Reference Ohm’s law on the interdependence of Current (I), Voltage (E) and Resistance (R).) Voltage and Current are dependent variable based on the internal resistance of armature/brushes and the back EMF of the coil windings.

10 10 2011
Infected Armory

What you say is true, but only in regards to the motor itself but over simplified when considering the whole system. Considering the motor free wheeling with no resistance, your information is correct. To expand on that, once a load is applied however, the current demand of the system would increase requiring more current to turn the motor. That is why you can have a system where it will pull an m110 spring with out tripping a 15amp fuse, but if you swap out the spring to a m120, then you find yourself needing a 20A fuse. Try overshimming a gearbox and then running it. The motor will demand more current to try to get the same amount of work done. Another thing to remember is amount of current needed to start the system moving is going to be greater than the amount of current needed to sustain the system once in motion.

10 10 2011
Mike Watkins

That, my friend, is called “motor torque equation” and is another
variable to consider as torque is expressed as a function of armature
current. There is a graph that shows the power/torque and power/speed
curve relationships well at: (Section 3.1)

Load torque does indeed, as you have alluded, affect motor current
up to the stall point at which point the rotational speed drops to zero and the
current reaches maximum whereas the motor’s unloaded torque condition
speed reaches maximum and current drops to the minimal level needed
to maintain speed. For our purposes (airsoft mechboxes), we operate
in the region in-between where torque equations and electrical equations
are in balance and therefore can be figured at any in point in the system.

Even under varying conditions of load torque, the motor’s performance is
nearly linear, though not perfectly linear. The motor still requires current
to operate at a certain speed and torque setting, defined by the motor’s designed internal electrical resistance, the load torque and the supply
voltage, hence my earlier assertion. We can vary voltage (using 11.1V or
8.4V batteries) or we can change load torque (as you stated…tuning the
drive train of the mech box for optimum power transfer). The two things
we cannot vary directly is the internal resistance and the current. The
Internal resistance is fixed by motor design and the current is simply the result of our applied voltage and load torque, hence the graph that
depicts power as the product of torque and angular velocity which is
halfway between the stall and no-load conditions.

We are both approaching the same conclusion but from different perspectives. We both, I think, see the cause and effect of voltage and
torque in our “AEG System”. I like to dive into the equations because it
is fun but there is also the old tried-and-true method of simply putting
a voltmeter and ammeter in the battery supply circuit and doing the
power calculations based upon the readings. That power is used somewhere is usually divided between producing heat and generating torque. Mech
box gurus (I am not one of those) strive to make their mech boxes as
efficient as possible to reduce system losses, just like you stated earlier.


14 02 2012

thanks for taking time to discuss this and it’s very well written. i have a question though. in my experience as an airsofter and a lipo user, the “c” term in a lipo batery is the discharge rate of the battery. however, is there any possible way to increase the discharge rate? example if you parallel 2 sets of lipos, this means that the “mah” of both batteries will add up right? would the “c” rate will add up as well? like each lipo have 2000mah (20c, 11.1v), when paralleled, it will became 4000mah and still 11.1v since its in parallel. will it became 40c as well? thanks :D

26 03 2012
Infected Armory

If you have identical cells (preferably from the same manufacturer), then you can increase the current output of the “pack” as a whole. You cannot increase the C rating of the packs, but by increasing the capacity (mAh), you will increase the current output capability. You do need to have the packs wired properly. In order to increase the capacity you need to wire the packs in parallel. If you wanted to increase voltage but leave the capacity the same, you would wire them in series.

10 03 2012
Jason Finn

hey man great article. very well explained in plain english, i like that. only thing is you say you gun reguires 22A to drive it. how do you know that, and how do i work out how many amps my gun needs to drive it.

26 03 2012
Infected Armory

You really need a meter that can measure the current draw. Most digital meters that people have laying around cannot measure above 10A or so, and it can be pricey to pick up a new one that can measure higher than that. If your gun is built right, most average builds will run less than 15A after the initial startup of the motor.

24 04 2012
Lipoly vs Nimh

[...] to first when asking about lipo batteries. And like I always say you should probably read it twice. Lithium-Polymer Batteries — Part 1 __________________ FREE Airsoft Gear [...]

12 02 2013
Crane Stock Lipo

[...] googletag.display('div-gpt-ad-1360119174578-5'); [...]

21 02 2013
Battery from battery king

[...] this, people on this forum are in desperate need of it: I'ts going to be hard to fit a 3s in a handguard. 2s is hard enough. But I don't buy those airsoft [...]

21 02 2013
KWA Full Metal KM4A1 - Page 3

[...] one). No issues at all. High discharge rates will not effect a gun's trigger contacts. Read this: With your reasoning, a 100C 500 mah battery is totally deadly to a guns trigger contacts but not a [...]

5 03 2013
Helical gears - Page 2

[...] this article please, it will teach you about LiPO batteries: googletag.display('div-gpt-ad-1360119174578-5'); __________________ WTS: CYMA AK47 [...]

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