It takes 8 "AA" batteries, mounted inside the top of the compartment. Definitely not an easy change out. I've tried several different brands of batteries (including Eneloop rechargeables) and every time I go to open it, the batteries are dead. The batteries don't last a week in the thing with no use. If you get one of these, get one with an AC adapter or plan on using the key every time. I'll sell you mine for $50 if you still plan to buy it....