Lithium Polymer batteries have been the ultimate game changer in RC, and if you're old enough to recall those dreaded NiMh / NiCd days of endless charge times and ultra low run times (shudder), you will count your lucky starts that we are in the age of fast charge, high power electric performance that is not only epic in power, but affordable as well. Thank you, China!
In the age of LiPo batteries, choosing a LiPo battery for your RC needs can be MASSIVELY overwhelming. Seriously. From voltage, mAh, charge ratings, discharge ratings, dimensions, brands and more, it can be a formidable challenge for an average RC enthusiast and a chasm-like expanse for someone new to the RC mix.
But don't worry - we're here to help. We've laid out the below info to help demystify the LiPo world and make your next LiPo purchase an enjoyable one, versus a frustrating endeavor that ends in pure Luddite rage.
mAh - It's the Fuel In the Tank.
When choosing the correct mAh (or capacity) of your LiPo battery, you want to make sure you're choosing the proper sized pack for your application - and we don't mean the physical size, although mAh does affect size. What we're talking about is what your application requires - i.e., what your aircraft, car, boat, etc was designed for.
The capacity / mAh of a LiPo battery is how much "fuel" is in the tank and is directly indicative of how much run time your battery will provide. More mAh equals more go, less mAh equals more no. So, why not pick the highest mAh pack possible? Well, because it won't fit, and it will weigh a proverbial ton. A massive mAh battery has no negative bearing on your application in terms of harm - it just won't fit, and it certainly wont go.
So, you need to make sure the pack you choose has the correct mAh relating to your application. This can usually be found via the manufacturer specs, and will be laid out in mAh (an example being 5000mAh) or sometimes in "Ah," which would be 5Ah when comparing to the 5,000mAh pack mentioned before.
Voltage - Choose Wisely.
From 1S to 14S batteries, voltage is a crucial variable in terms of application. If you choose poorly, you will end up with a rather sad and expensive pre / post 4th of July celebration that will be quite maddening, with the off chance of catching something on fire. Not really a great outcome unless you're a touch on the cold side, so be sure to pay careful attention relating to voltage.
Again, the application at use is crucial, with each application (airplane, heli, drone, car, boat, etc.) having a different voltage requirement. The higher the voltage, the more power & r.p.m. the motor will reach in relation to the application of use, so it's imperative that you reference the manufacturer specs to make sure you're using the correct voltage of battery. If you choose the wrong voltage, you could either damage the electronics in question, or in the case of choosing a lower voltage than required, your model or aircraft will lack serious power and will not operate correctly.
Some applications allow you to vary the voltage, allowing the use of differing voltage packs to take advantage of more power, if you so prefer. In a case like this, stepping up to a higher voltage pack will equal more speed, power and overall performance, as the increase in voltage causes the motor(s) to spin at a faster r.p.m. A bonus to this is higher voltage setups pull less amperage, so you needn't depend upon high C discharge packs for maximum power. So, if you're Ricky Bobby fast and you have the option to select a higher voltage pack, you can choose the higher voltage range to push the envelope of speed & power.
Discharge Rating - The Power That Lies Within.
25C, 35C, 45C, 65C, 95C - what in the world does this all mean? Quite simply, this is a rating of how many amps of power the battery can deliver. However, before you jump to the easy conclusion of these numbers being an exact value of the amperage your LiPo battery can deliver, a bit of math is in order. Don't worry, though - it's easy math.
To determine how many amps your pack can delivery is quite simple. Just divide the mAh of your battery by 1,000 and multiply that number against the C rating - that's it. Let's use a 5000mAh 45C battery as an example. 5,000 divided by 1,000 equals 5 - easy enough, right? Now multiply 5 times 45, and you have 225 as your final number. This means this particular 5000mAh 45C battery can consistently deliver 225 amps of power - if asked to do so. The battery will only deliver what's asked of it, so if your application is drawing less than that final number, you're good to go. However, asking your pack to give everything its got is a recipe for a short battery life, so it's always best to choose a battery that has more amperage on tap than what's needed, which allows your battery to live a long, healthy & happy LiPo life.
But what happens if the battery has more amperage than what's required? Nothing bad - the battery will be much better off and won't have to work so hard, equating to a longer life. But, this doesn't mean you need to choose the highest C rating pack, because higher C packs cost more, and they also weigh more, too. Best bet is to simply make sure that your pack of choice can deliver the amperage your application requires with a good dose of amps to spare - your LiPo will thank you for it.
Charge Rating - Fast Charge Bliss or Screaming Toddler Delays.
The beauty of most modern day LiPo batteries is being able to charge them quickly, leaving you with more time having fun and less time staring at your charger as you await a chorus of beeps to let you know the fun FINALLY begins. And with LiPo packs that have a 5C charge rate capability, we're talking about charge times of less than 15 minutes, compared to a full hour with 1C packs. Ouch.
So, what does this "C" mean? Didn't we already cover this? Yes - we covered the Discharge rating of the pack. The Charge rating is the other side of the coin, and is quite important when choosing your LiPo pack, and most importantly, charging your LiPo pack.
In terms of charging your LiPo battery, the amperage is what counts. Simplified, the more amps you can pump into your pack during charging, the faster your pack will charge. But before you max out your charger for the fastest charge possible, you need to make sure your battery can handle it, and you need to know what the maximum amperage your battery can be safely charged at to prevent battery damage or a potential fire.
As with the Discharge rating on your pack, the same math from above applies. To determine the maximum safe amperage your pack can be charged at, divide your mAh by 1,000 and multiply it against the charge C rating - that's it. So, if we take our 5,000mAh battery example from above, 5,000 divided by 1,000 equals 5. In the case of a 5C pack with a 5C charge rating, 5 times 5 equals 25, equating to a safe 25A maximum charge rating. So, if your charger has the power to actually charge at 25A of power, you could safely charge this 5000mAh 5C pack at 25A of charging power, equating to an ultra fast 15 minute charge time to get you in the air and having fun.
No matter what battery you own, be sure to carefully check the manufacturer specs relating to charging, as many batteries on the market are not designed for a 5C charge rate. Usually the charge "C rating" is listed on the back of the battery, and can be anything from 1C, 2C or more. Charging beyond the manufacturer charge rates is asking for trouble. It's not worth it and will no doubt damage the battery, so follow whatever the manufacturer states to keep things safe.
Dimensions - It's the Fit That Counts.
The last component to our story is very straight forward and leaves little explanation required. However, when choosing your LiPo battery of choice, dimensions are crucial to the proper fit of your LiPo, so getting it right can (and will) make all the difference in the world.
When choosing your LiPo, don't just make sure it fits - make sure it fits properly. An area too tight (especially with sharp, carbon fiber frames) can cause a battery wire (or the battery itself) to be damaged or punctured when trying to force an ill sized battery into an area it wasn't designed for. We've seen this happen before, resulting in a wire being cut on a sharp carbon frame, resulting in the battery shorting out and frame damage to boot. You want plenty of room, a nice, solid fit, and the ability to insert and remove your battery without the necessity of a crowbar, which is indicative that you may have purchased a battery a touch too large.
All in all, keep a close eye on the physical dimensions of your battery before you click the "buy" button, and pay attention to weight as well, as this will play a part in the way your application performs. If you follow all the tips above, your next LiPo shopping experience should be far less mysterious, equating to the perfect LiPo battery for your RC needs.