I procured another battery. I had to pick up a cheap and dead 520 to get the battery. Craziness.
I took this one apart and as usual the cells were leaking everywhere. Part of the ribbons were eaten through. This board also had a different layout.. different than mine, different than
@aladds, different than a picture I saw of
@3lectr1cPPC's battery. The Apple chip tested ok, unlike mine this one had infinite resistance across pin 14 and 28.
I took the cells out, cleaned up the insides, put new wires in instead of the half eaten ribbon, and placed my NiMH AA's inside. Battery was detected by my 540c but both Lind and EMMpathy were complaining about corrupted memory. Tried numerous times with both utilities but same error.
I had an extra memory chip from when I replaced the memory on my other battery so I replaced the memory chip on this one as well. Popped it in and Lind was able to write over the whole thing and get it right. EMMpathy was happy with it also after Lind had rewritten the memory. So all good there.
As of right now, the new battery seems to be working. My 540c can boot and run on the battery and it seems to be holding.
I did find one issue though. My stock power brick seems to be going bad. The Vmain side seems ok but the Vbatt side seems to be failing as during charging, it keeps stopping for a bit every minute or so.
Anyhow, back to this dead 520 I got. The power adapter that came with it is dead. I cracked it open and I don't see any obvious leaking from the caps but the fuse is dead. Need to figure out what the rating on it is and try replacing it first. But the case broke apart into lots of pieces, the plastic was really brittle. In fact, I used my hand to open it as only a little pressure actually caused the seam to crack.
As for the 520, screen is trashed. It's bubble, has dark marks, and looks like the top layer is peeling off. Not sure what happened to this thing. The 520 also won't start, no power. I took the thing apart and found the power socket was loose. Resoldered that and the 520 powered up. Hard disk, floppy drive, keyboard, touchpad, all seem to work. But the screen is dead. The backlight works but nothing is displayed. Figures, since the outside like I said was completely trashed. I had to use the display off my 540c to test this thing.
At least I got a working battery. And I've got a bunch of extra parts now.