As a Battery Pack most commonly used on laptops, 6-cell lithium battery is specially designed for laptops. 6-cell lithium battery is combined with 18650 battery cell, whose current voltage is 3.7V or 3.6V.
6-cell lithium battery with 3.7V has two combination ways: 7.4V and 11.1V. Take 18650 2200mAh battery cell for example:
7.4V Lithium Battery Pack refers to 6-cell lithium battery in 2S3P combination. That is, first connect three battery cells in parallel, and then connect two sets of paralleled battery cell in series. Rated voltage of this 6-cell battery pack is 7.4V and nominal capacity 6600mAh.
11.1v Lithium Battery pack is 6-cell lithium battery in 3S2P combination. First, connect two battery cells in parallel, and then connect three sets of paralleled battery cell in series. Rated voltage of this 6-cell battery pack is 11.1V and nominal capacity 4400mAh. 11.1V 6-cell lithium battery is often called 12V Lithium Battery.
3S2P and 2S3P combinations can attain different voltage and capacity. This is determined by series and parallel law: for lithium battery in series, total voltage equals sum of single battery voltage and total capacity is the same as single battery capacity; battery in parallel is on the contrary. Thus voltage of 3S2P battery is 3.7*3=11.1V and capacity is 2200*2=4400mAh; similarly, voltage and capacity of 2S3P battery is 7.4V/6600mAh. These two parameters are often marked on 6-cell lithium battery because they determine output power of a 6-cell lithium battery.
Owing to the fact that output power of a lithium battery is 2200*3.7=8.14wh, output of 6-cell lithium battery is 8.14*6=48.84wh. in other word, work capacity of 7.4V and 11.4V 6-cell lithium battery is the same but their working voltage is different.
If combined with 3.6V lithium battery cell, there are two voltages on 6-cell lithium battery: 7.2V and 10.8V. Considering above 7.4V and 11.1V, totally there are only four kinds of voltage. Compared with voltage, 6-cell lithium battery capacity is various because single 18650 battery cell can be made to many different capacities.
