The NiMH batteries offer a solution to replacing batteries, and they don’t have the memory issues NiCads have and are very powerful at 1800 mAhrs.� The SuperDroid Trekker requires 8 AA Batteries.� The package also includes a charger with a plug end that connects to the OOPic II Expansion Card or the OOPic-R Expansion Card.� The AC plug can also be used to power the Trekker.���For just the transformer, follow this link.