How to find the laptop battery specifications
There are different types and sizes of laptop batteries. To determine what laptop battery you have, remove the battery from the laptop and look at the bottom or top of the battery.
As can be seen in the picture, this Dell battery shows that it is an Li-ion battery, has a model number of Li-ion II, rating of 10.8V, 4050mAH, Part number, and a charging current of 2.5A.
If your battery is not labeled or you're unable to read the information on the battery consider using a third-party utility that's capable of giving you detailed battery information. For example, BatteryCare is a free software utility capable of doing this.