Batteries come in various capacities.
The capacity is measured in 'mah' (Milli-amp hours) and denotes how long it will last once fully charged.
You can buy regular eCig batteries as small as 650mah, and 900mah.
Most outlets provide 650mah batteries in their starter kits and as replacements because they are cheaper to supply and easier to sell.
At Aussie eCigs, we feel the performance of the 650mah & 900mah batteries is disappointing for users, so the smallest capacity battery we sell is the 1100mah.
Higher capacity batteries are also available by request.