It's often not easy, either. It very much depends on the battery and the used controller. Make sure to always have enough voltage on the controller, since it mi

It's often not easy, either. It very much depends on the battery and the used controller. Make sure to always have enough voltage on the controller, since it might shutdown on power loss, leaving you with a battery with '0.0Wh capacity', regardless of the new cells. Also, some battery packs might require you to solder the cells, which is not for the faint of heart.