Lego Exclusive Set 9798: Rechargeable Battery

No more disposable batteries! Add the rechargeable battery to your LEGO MINDSTORMS NXT robot and end your need for AA batteries! Rechargeable battery is lithium. Requires #9833 Transformer, sold separately, to recharge battery. Please Note: Building instructions for NXT models do not include instruction for incorporating the rechargable battery. This battery will increase the depth of your NXT intelligent brick so you will need to adjust your models accordingly.