Every 100mah is about 1 hour of moderate
vaping with standard resistance atomizer or cartomizer
I consider moderate
vaping to be
vaping less than 1/2 the time.
Then the following will reduce that amount of time
- heavy or constant vaping could cut the time in 1/2
- dual coil carto or atomizer like 1.5ohm could also cut it in 1/2
- less extreme LR atomizer or cartomizer (say 2 ohms) may reduce the time by 1/3
In extreme cases the time could be very short - like one guy was vaping 900mah batteries down in 2.25-2.5 hours by using dual coils and vaping constantly.
Re spares - for any ecig you depend on, you should have spares of everything: battery, charger (I also like having a charging cable at work), atomizers, cartomizers, juice