Like mentioned, you must make sure the voltage (3.0v, 3.7v, etc) matches what your device requires (or totals up to what it requires). Atomizers should not be run over 5 volts in most cases so if what your wanting to use will be over that, say 6 volts, you might want to rethink.
A good rule of thumb is keep your voltage below 5 volts and your atomizer should be happy.
maH is just how much current the battery will produce per hour. The more the better. For instance an 800mah battery will last longer than a 130mah battery. If I remember my electronics correctly, maH means that an 800mah battery will produce 800 millamps of current for one hour, constantly for one hour. Of course with ecigs, the battery is never on constantly for one hour, only seconds at a time.
As far as battery chargers are concerned, never mix types of batteries with different chargers. Lithium chargers are for lithium. NiMH is for NiMH. NiCad is for Nicad. The reason for this is that different types of batteries require different methods of charging, to keep it simple. I could go into a lot more detail but it's not neccessary. Just remember that each has it's own and must be used as such.
Each battery type needs different charging currents and voltages to reach and each battery type is different.
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