Issues with VMU battery connection(?)

[Voll]

Hello, I've been using VMUs regularly for about 3 months now (i.e. taking them with me outside), but a few of the ones I have have had issues with suddenly rebooting or appearing dead when the batteries still work. I can't tell if it's the same issue for all of them, or just similar looking issues.

My translucent Pink VMU had worked pretty flawlessly until very recently, where now the batteries seem to lose contact randomly, and pressing down on the backplate can either turn it off or cause it to reboot--it's a bit inconsistent.

My translucent Green VMU has had issues since the beginning. The backplate has never sat correctly, appearing that it's bulging out very slightly in comparison to my other ones. I've always had to fiddle with the battery placement to get it to work without rebooting super easily.

I just recently got a Strawberry VMU, and I cannot really determine the issue with this one on the surface. The batteries sit just fine in the compartment, but I still have similar issues.

I've researched on the topic a tiny bit, but I haven't really found a lot of solid advice. I've tried tightening some of the inner components, and that hasn't fully fixed the issue. I've also read that cleaning up the electrical contacts might help, but I don't have any cleaner on me at the moment, and I'd rather not do something like that until I can deduce that that's the most likely solution to my issue. Is this a common issue? Are there any other solutions that are worth trying other than what I've already seen? I can provide some photos if needed, but the differences are so minor that it's hard to show with a camera.