I meant to answer some of your battery questions from last night... but got caught up with trying to see Comet Lovejoy and forgot
The batteries we typically use have what is referred to as a nominal voltage of 3.7v ... that isn't what it's voltage is when they are fully charged. It is their "middle" voltage charge they have... it is also referred to by some as their storage voltage since it's the voltage they are most stable at. When these batteries have a full charge... they should have 4.2v and no more ( charging beyond that is very hard on them and ends up limiting their potential lifespan ). When they are "empty... they still have about 3.2v of charge left in them but taking them down to that level is also hard on them... most recommend only taking one down to 3.4-3.5v at most.... the 3.4v equates to them having used 80% of their total capacity.
The capacity of a battery is listed in Amp Hour ( ah ) or Milli-Amp Hour ( mah ). 1 ah is equal to 1000 mah. If you use up 80% of the batteries capacity ( which would leave about 3.4v ) then with a 1000mah battery you will have used 800mah of it's total charge.
The amperage discharge rate for a battery is rated with a C rating. The C rating is based on the total capacity of the battery so a 1000mah battery with a 1C discharge rating can discharge at 1 amp ( ie 1000ma )... at a 2C rating it would be able to put out 2 amps of power. There is also a charge rate for the battery also using the C rating method. The discharge rating is usually much higher than the batteries charge rating. So knowing both the charge and discharge C rating is important but they still often don't tell us both ratings, I suspect for marketing reasons. Another marketing ploy we see is a battery just advertised at it's maximum burst amperage instead of its max constant discharge amperage... so watch out for this... it just means those types of batteries can put out that amperage for just a short while usually a few seconds at most.
Now let's put some of that info to use in an example battery... the new AW 18650 2200mah battery let's say. It's max constant amp output is 20a and it's max charge amperage is 2.2a ... that means the discharge rate is about 9C ( 2.2a x 9 ) and the max charge amperage is 1C ( 2.2a x 1 )
Most, but not all... batteries can be charged at 1C safely but if you don't know... don't exceed 500mah ( 1/2 A ) just to be safe.