What the hobby/RC world calls a “6S” battery is six lithium-ion (typically Lithium Polymer, or “LiPo”) cells, wired in Series, then packaged together with a 7-pin balance charging connector that allows a charger to sense/charge each cell individually, along with a fat 2-pin connector (often XT60 format) that delivers the series output of the battery as a whole.
What is an amp-hour?
An amp is a measure of electrical current, and the hour indicates the length of time that the battery can supply this current. A 2.2Ah battery can supply 2.2 amps for an hour. If the lipo battery 2s must supply more amps, because a bigger device is connected, it will last for a shorter period of time; if the battery is supplying less amps, it will last longer. The problem with thibs method is that it doesn’t give a complete picture of the total energy stored. It is easy to find cases where two different batteries with the same number of amp-hours will have completely different amounts of total energy.
What is the difference between watt-hours (Wh) and amp-hours (Ah)?
The equation for power is
watts = amps x volts
and for energy the equation is
watt-hours = amp-hours x volts
What if I don’t have watt-hours?
3.7V per lithium-ion cell (RCs use a single cell (3.7V), laptops typically use 3 cells in series (11.1V)
3.2V per lithium-ion iron phosphate cell (multi-cell LiFePO packs are typically configured as 4-cell or 12.8V)
1.5V per alkaline cell
1.2V per NiMH and NiCad cell
2.1V per lead-acid cell (car batteries are 6-cell (12.6V) and some golf carts are 3-cell (6.3V))
The capacity of the battery, in milli-Amp hours (mAh) is usually its most prominent rating, but there are a few other interesting numbers. For an example, let’s use the cheapest lipo battery 4s on Gens Ace at the moment: B-Grade 3000mAh 4S 20C Lipoly Battery
3000 mAh is the capacity, the nominal total amount of energy stored in the cells in milli-Amp hours.
22.2V is 3.7V (nominal voltage per cell at 80% capacity) × 6. You would expect to see higher resting voltage at a full charge (around 4.2V per cell), and lower under load. You should never go under 3.0V per cell under load (i.e. 18V for the whole pack), you can permanently damage the cells.
“20C” discharge rate means it’s rated for discharge at 20× the capacity normalized to 1 hour to full charge. So, if you were charging at 3A for one hour to reach full capacity, you could discharge at 20× that, or 60A. Keep in mind that 60 amps is a lot of current!
“5C” charge rate means you can charge it at 5× the current indicated by a full discharge in 1 hour. So, it should be safe to charge at 15A (3A capacity, times the “C” rating of 5)