The VMU has two flat batteries inside of it. These will without a doubt go dead in no time flat. Ive had several VMUs and all the batteries have died in a relatively short period of time. These batteries can be bought at a local flea market for a few bucks each, but it really isn't worth the price, since you can buy a new VMU for under $10 these days anyway. If you do want to buy new batteries for it, just unscrew the screw on the back of the VMU and take one of them out and bring it with you so you can show the person at the store the type of battery you want, since they probably won't know if you ask them for a VMU battery. Unless you have a game that has a mini game in it, there isn't really much use replacing the battery, since it doesn't affect the save feature. But that's up to you 😉
