If you are one of those people who literally go through the spec sheet of a laptop you will definitely come across the battery specification. Battery specifications can be 42 wHr 3 cell or 66 wHr 4 cells. It depends on the laptop manufacturer some laptop even have 6 cells, 9 cell or 12 cell batteries.

Cells are basically pairs of batteries similar to AA batteries connected in series to give you a single laptop battery. So a 3 cell laptop battery is just 3 pairs of batteries connected in series. The same applies to a 4 cell laptop battery.

Note: The wHr/mWh/mAH is for the whole laptop battery, not individual cells.

Basically the more cells a laptop battery has the longer the battery life. Two laptop batteries; one has a 42 wHr 3 cell and the other is a 42 wHr 4 cell. The 42 wHr 4 cells are going to outlast the 42 wHr 3 cells