I had that same exact problem a couple of weeks ago. When charging, the thing would show multiple jumbled batteries and the screen was all screwed up and backward while I tried to use it. I thought it was because it got too close to a welder at work or something. I guess not. I replaced it too, but that's definitely odd that both of ours did the same thing.
Also, I am doing a little work right now to build my own stealth mics and battery box. This little unit is just too small to not make a killer stealth rig. I'm going to build panasonic capsules into headphones, so it looks like I just have an MP3 player and some headphones.
I have to include an op-amp in the battery box in order to get the voltage up high enough for the Gmini's line in. The whole thing runs off of just two AA batteries, so I can use the same rechargable ones I use in my DAT. Looks like I should be able to get the whole thing done for about $20 or so. From the specs on the caps and amp that I'm using it should sound really good. From initial tests on the proto board it sounds good and works fine. I'll post plans, results, etc. if anyone is interested.
Riley