At present the majority of laptop batteries are based on industry-standard batteries, generally divided into cylindrical and square.

Cylindrical-shaped batteries are bigger than AAA batteries, while the square batteries are roughly equivalent to the size of a Zippo lighter.

The current capacity of the mainstream batteries: cylindrical for the 3.6 ~ 3.7V/2000 ~ 2200mAh, square for the 3.6 ~ 3.7V/1800 ~ 2000mAh, so the battery in the end used how many batteries can be inferred according to the above figures, such as the IBM ThinkPad T40/T41 standard battery is 10.8V/4400mAh, then the number of batteries is 6, three-string, and two parallel, namely: the three energy-saving core series to be 3 X 3.6V = 10.8V, the two sets of series after the batteries in parallel and then get 2 x 2200mAh = 4400mAh.

The IBM ThinkPad T40/T41 enlarge battery is 10.8/6600mAh, then the batteries number is 9, using a three-string, and three parallel way, namely: the three energy-saving core series to be 3 X 3.6V = 10.8V, the two groups after the batteries in series and then parallel to be 3 x 2200mAh = 6600mAh.

Generally speaking, the difference between battery the enlarge and standard battery is that an increase of the number of batteries connected in parallel to increase capacity.