Voltage, capacity and discharge rate are the three main numbers you will need when going battery shopping.
VOLTAGE:
LiPo battery cells are rated at 3.7 volts per cell. The benefit here is fewer cells can be used to make up a battery pack
Here is a list of LiPo RC battery pack voltages with cell counts. 2-6S in parenthesis means how cells hooked in series(S) that the battery pack contains.
·7V lipo battery = 1 cell x 3.7 volts (1S)
·4V lipo battery = 2 cells x 3.7 volts (2S)
·1V lipo battery = 3 cells x 3.7 volts (3S)
·8V lipo battery = 4 cells x 3.7 volts (4S)
·5V lipo battery = 5 cells x 3.7 volts (5S)
·2V lipo battery = 6 cells x 3.7 volts (6S)
You may also come across packs or cells hooked up in parallel to increase the capacity. This is indicated by a number followed by a “P”. Example: 2S2P would indicate two, two celled series packs hooked up in parallel to double the capacity.
So, if a model calls for a 11.1 volt battery – just ask for a 11.1V lipo battery or a 3 cell lipo battery
CAPACITY
Capacity indicates how much power the battery pack can hold and is indicated in milliAmp hours (mAh). If you want more flight time, increase the capacity of your battery pack. Unlike voltage, capacity can be changed around to give you more or less flight time. Naturally because of size & weight restrictions, you have to stay within a certain battery capacity range seeing that the more capacity a battery pack has, the larger and heavier it will be.
DISCHARGE RATE
Discharge rate is how fast a battery can be discharged safely. In the RC LiPo battery world it is called the “C” rating.
Most RC LiPo Battery packs will show the continuous C rating and usually a maximum burst C rating as well. An example might be something like “Discharge rate = 25C Continuous/50C Bursts”.
The higher the C rating, usually the more expensive and even slightly heavier the battery gets.
As a very general guide line, 25C to 30C discharge rated packs are the norm for most 250-450 size electric helicopters with general to light sport flying in mind. For larger birds, 30C to 35C discharge rated packs are a safe bet (again for normal to light sport). Once up to aggressive sport or 3D, that is where the 40C and up discharge rated packs come into play. Of cause the battery will run cooler and have longer life span if it is double of the C rating you intend to pull out of.
All this said, RC LiPo packs are coming down in price all the time. If you find a 35C pack for the same price as a 25C when that is all you need, go for the 35C pack – it will run cooler and have a longer life span. Like most things, pushing a Lipo pack hard close to its limits will wear it out and reduce it’s useful capacity in very short order. If however you get a pack with a C discharge rating at least double of the maximum you intend to pull out of it; with proper care, there’s no reason you shouldn’t be able to get at least 400 charge and discharge cycles out of it with average degradation.