Lithium-Polymer Airsoft Batteries
Airsoft is a world full of old technology and an industry of slow moving innovation. Look at the batteries we use. Up until recently, most Airsoft Electric Guns (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:
- Lipos WILL explode and are very dangerous to use
- Lipos are too powerful for anything but a heavily upgraded airsoft gun.
- Lipos require a lot of babying
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 latter 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 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 your 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!
Enough of the past, let us venture on into the future where before us lies the land of li-poly happiness and reliability! Wait, did I just use li-poly and reliability in the same sentence? You bet your granny's muffins I did. We've already proved that you have to abuse them to create that great big ball of fire that will not only kill your battery, but swap your two ply toilet paper for single ply! Now you're asking, since they're reliable and my toilet paper is safe, how do I take care of li-poly batteries? Thought you'd never ask.
First let's go over the general construction of a Li-Poly pack. There's really not much to understand here other than, like NiCad and NiMH batteries, it's a group of cells wired / soldered together. As usual, you have a power connector, but unlike the other battery chemistries, you also have a balancing connector. More on that later.
Lipos require a lot of babying
Well, here's the cold hard truth. They don't. They do require a bit more effort to maximize your output and use, but the rewards of using a li-poly far out weigh the slight bit of extra work. Let's break it down into the main parts of battery maintenance.
Really, there's nothing new here. Just like NiMH or NiCad batteries, don't drop them, puncture them, set them on fire, stick them in a fire, overheat them, or wear on your forehead and play William Tell with a Barret 82A1 rifle. One more thing, don't leave a battery of any type charged without someone present.
Charging a li-poly battery does require a charger that. well, can charge li-poly batterie. These are not as common as your NiMH or NiCad chargers, but there is an increasing number of them. What you pick is up to you. They sell some as cheap as $35 that are li-poly specific at HK airsoft stores, up to $130 chargers that can handle any battery type. As far as chargers go, you really get what you pay for. Having a charger that is able to tell exactly what the battery is doing every moment while charging, and adjust accordingly is a real benefit not only for li-poly batteries, but all battery types. I personally use a Triton2 made by Electrifly. This is a pricey unit but will handle any battery I could currently need for airsoft, and it has 10 memory settings. But, that's another review, so we'll keep moving forward.
One optional, but highly recommended bit of equipment is a Balancer. That sounds like a fancy piece of kit, but in reality it's very simple, and pretty cheap (about $30 for the one I picked up and I'm sure there are cheaper ones). A balancer makes sure all the individual cells that make up your battery pack are all charged to the same level. This is important as you'll find out later in this article. Balancers work by taking voltage from one cell, and moving it to another till they are at the same charge level. Easy. For the most part, you just plug in the balancer to the battery, press one button and presto after a few minutes your pack is balanced and ready for charging.
Another piece of equipment you need is a Liposack of some sort. This is just a precaution. If your lipo has been damaged, and you are unaware and are trying to charge it, there is a chance it could ignite (just like any damaged battery). Because lipos do ignite violently, the use of one of these bags is recommended. Just place your lipo in the bag with the wires hanging out. Hook it up to your charger, and charge. If the battery were to fail, the bag would contain the fire for the most part, and vent out the excessive gas. Again, the likelihood of this is pretty low, but better to be safe.
As far as charging goes, it will depend on your charger. Mine just asks for the capacity of the battery and the voltage. Once I put those two numbers in, off it goes charging my battery. With the Triton 2, my 2200mAh battery charges in about 1 hour.
Some balancers work through the charger. I use the Equinox balancer. This one can be used with or without the charger. The beauty of this is that it keeps the pack balanced while charging.
Now I said I would get back to the balancer and why you should balance your packs. Here's the deal. Li-poly cells have a lower discharge limit of 3v for most manufacturers. If you go below this, there is the potential to damage your battery and prevent it from ever charging again. Let us look at an example.
Say you have a 2 cell pack. That's 7.4v total power. Say cell one has 3.5v in it, and cell two has 3.1v. What happens is that you can still run your pack, but cell two will dip below the 3v minimum, and could be permanently damaged. If you balance the pack before you use it, or before you charge it, you'd end up with two cells that are each at 3.3v. They will hit the 3v minimum at the same time. This maximizes the capacity you can get out of your pack by running all the cells down at the same time instead of having to stop playing to charge backup because one cell is too low.
This all sounds complicated, but I'll wrap it up in a neat package for you at the end.
Low voltage Protection:
Remember what I said before about the fact that li-poly batteries need to be kept above 3v? If you're using a li-poly on a gun with heavy demands or for multiple days, I suggest checking the voltage on it periodically. This is easy to do with a multi-meter. Just use the balance tap to check the voltages. If you want to make it even simpler, there are devices you can plug into the battery that will use led's to show you the charge of each cell, and warn you if you're getting close to the low end. There are even units that will beep/buzz so that you have an audible cue if your battery starts to reach the bottom of the barrel and needs charging. So no worries there if you don't have a multi-meter or don't know how to properly use one.
Storing a li-poly is pretty straight forward. You can keep them all in a liposack for protection, but the concern here is that if one pack goes, all your packs go. I've heard of people purchasing nomex socks and using them instead of a liposack, but a pair of nomex socks seem to cost just as much as a liposack. My suggestion is to use a separate liposack for each battery and put them in a metal ammo tin. Of course, if you're willing to risk it, you could just store them in one liposack and toss that in an ammo tin. Just weigh your cost vs. potential losses.
Okay, so let's sum up what you've got to do with a li-poly battery to make it usable and use it.
- Charge It - Do this with a balancer if you have one. Some chargers might have a balancer built in and you wouldn't need to worry about a balancer. Some balancers need to be used in a separate step.
- Balance your battery
- Put it in your AEG and abuse your enemies!
- Store it for use later.
If you stick to that, and keep that voltage above 3v per cell (easier than it sounds), then you'll have a battery that will far outlast your competition.
Breaking Down the Jargon:
Let's talk a bit about picking out a li-poly battery. After KWA came out with their "Li-Poly Ready", M4 (which is a bit misleading), airsoft retailers began to claw their way into the li-poly market. The most common offering I see is one by Firefox, but Evike and others are marketing their own in-house brands as well, and it looks like King Arms is about to start in as well. In the end these all probably come from the same factory, but that is neither here nor there. Let us dissect the nomenclature of the li-poly battery. We'll start with an example:
7.4v (2S) 2200mAh 25C
Seems confusing, but it's not.
7.4v: This refers to the voltage of the entire pack. Since each cell holds 3.7v, this pack must have 2 cells wired in series. Common pack voltages you'll see for airsoft use will be 7.4v and 11.1v.
2S: This refers to the number of cells in the battery pack, and the fact that they are wired in series. If they were wired in parallel it would have said 2P instead.
2200mAh: As usual, this is the capacity of the battery in milliamp-hours. The larger the capacity, the longer the battery will last before needing to be recharged.
25C: We talked about this earlier - it's the discharge rate. If you don't remember what the discharge rate is all about please go straight to part one, do not pass Go, and do not collect anything but nasty looks from the gnomes who write these things.
Now that we have the nomenclature down, we need to concern ourselves with the choices that are out there. First let's see where we're putting our pack and determine how much space we have to work with. With that sorted out, we know our physical space limitations. Now let us look into what it is that we want out of the AEG we're putting this into. If you're looking to create an ROF beast, then an 11.1v battery is your goal. If you're simply looking to replace that mini 8.4v or 9.6v NiMH or NiCad battery, then a 7.4v li-poly should fit the bill nicely. Your next concern is capacity. How do you determine the capacity you need? Well, it depends on a lot of things, and there is no real concrete answer to this. If you have a gun that runs at a high fps, you're going to need more capacity as it's going to be used up more quickly. Now looking at reality, I've seen an m14 DMR running semi-auto only, go through 700 rounds and the 2200mAh li-poly battery was still almost full. Your real limiting factor here is space. You can use a battery as big as the space you have to fit it in, but you might want to consider using this battery in more than one gun, so you have to fit the smallest denominator.
Now onto the discharge rate. This is where the money is. We've done the math on this a few times, but we'll do it one more time, but with an actual battery. Let's look at the Firefox brand li-poly battery that is available at several HK retailers. The specs read as follows:
11.1v 1600mAh 12C
Doing the math we find out that this pack has a continuous discharge capability of 19.2A. What a failure. Why spend the money on a charger, a balancer, and a li-poly for a discharge rate of 19.2A? Now let us look at a 7.4v li-poly made by Elite for just $6 more:
7.4v 2200mAh 30C
Doing the math, you get a 66A continuous discharge capability! So sure, we drop back to 7.4v, but we're back to supplying the motor and drivetrain the current it needs to run at 100%! So in this case, the 11.1 wasn't a win because of its low C rating. Once you've decided on capacity and voltage, you need to consider the discharge rate carefully. As proven here, the low discharge rate is a real deal-breaker for the Firefox batteries!
So how big of a C rating do you need? Good question. Really you just need to make sure that your battery can put out at least 30A CONTINUOUSLY. Ignore peak ratings, as they don't play a part as much as the continuous rating. If you can supply more than 30A with the battery of choice, that's fine. Remember, you're motor only takes what it needs.
Another important aspect of buying li-poly batteries is the retailer. Me personally, I prefer to buy my li-poly batteries from RCLipos.com, as their service is top notch and they are knowledgeable about the product they sell. Buying from some of the HK stores could leave you high and dry if you have a question about the batteries, or need help after the sale. Stores that supply RC hobbyist tend to provide the best service and be more knowledgeable.
One more thing.
One thing that I neglected to mention is that most li-poly batteries come without a power connector. While they have power wires, and a balance connector, they often are power plugless. This is easily remedied by soldering on a pair of Deans connectors (my connector of choice), or crimping on some Tamiya connectors (the bane of my existence). Honestly, if you're using Tamiya connectors, you're hurting yourself by using a poor quality connector with a high quality (and output) product.Now, if you're afraid to put on your own connectors, or don't want to deal with it, many RC battery stores will put the connectors of your choice on the pack for an additional charge.
Well, we're pulling into the station here at Li-Poly Euphoria, and boy has this been a trip. We know now that most of us are running our AEG's at less than 100%, are using underpowered power supplies (batteries), have found out that li-polys are innocent of AEG murder in the first, and now know how to pick out a li-poly. We've seen the cost of switching to li-poly batteries and realized that it's not unobtainable. But wait.. yeah you in the back. What's you're name? Doubting Thomas? Well, I thought our little trip to Li-Poly Euphoria would convince you that NiMh and NiCad technologies were a thing of the past, but that's fine. Stick with your outdated ways, if you so desire.. but you can never claim ignorance again.