Okay. I've had my DC since January, and I want to do stuff with my VMU. However, I can't turn it on outside of the controller. Does it need the cap on in order to turn on? I didn't get a cap with my VMU (bought it used).
IIRC it does need the cap because the cap contains one of the battery terminals... it is possible to mod it to take other power sources, but I'm not sure where to find instructions to do so. When it's in the controller, it's powered by the Maple Bus.
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
The cap isn't required to make it work. It has no terminals in it, it's just a piece of plastic. I tested it just now with a brand new VMU fresh out of the package and it functions without the cap on. The only purpose it serves is to keep dust out of the contacts.