Wow, thanks for that info. I would have thought you could still use the charger plugged into the wall even if the battery pack didn't work. Guess I'll never open it then. I've been using rechargeable batteries with my 15 minute quick charger and they last all week, so it's all good.
Hey, if it's never been used, then I'm sure it would work fine for at least a year or two... the real issue is that those '90s battery packs use NiCd batteries which don't last as long as the rechargeable styles that are used now.
Anyway, I'm not actually 100% sure that that's true. What I do know is that while I can get those battery packs working, but they're INCREDIBLY touchy, and reset pretty much constantly, when plugged in or not. I have to angle the plug a bit to get a reliable on, and of course then I can't really hold the system. I've heard that this is a common issue and might be a problem with the battery pack itself (when it can't hold a charge anymore, that is) and not the GB.
Also, of course, it's only for the original-model GB. All other models use different power supplies, so you can't use that with a GBC, GBA, etc. anyway, even if it's working perfectly. And the original GB gets pretty good battery life... 35 hours on 4 AAs, according to the manual, and I believe it. But anyway, there's not much reason to be using the original model GB too much, games blur so much on that screen that many of them are barely playable. I liked it at the time, and still use the original GB once in a rare while, but that blurring really is an issue, compared to a nice, nearly blur-free screen like the GBC or GBA have.