The Lulla doll sound unit uses two AA batteries. You can use both alkaline and rechargeable. Do not use Lithium batteries. Please note that rechargeable batteries can be bigger in size and some brand types might not fit the sound unit. Good quality brands that do fit the Lulla doll sound unit are for example Eneloop and Ikea rechargeable batteries. Two AA alkaline batteries can last for up to 300 hours in the Lulla doll. The time duration depends heavily on the quality of the batteries and the difference can be up to 85%! Better quality batteries cost more but then again they are more reliable and last for longer. Rechargeable batteries do not last as long as they are 1.2V (regulars are 1.5V). On the other hand you can use them over and over again making them the best long term investment plus they are better for the environment.