Got my battery today. It appears to be charged. The charging circuit appears to be working without a problem with the stock AC adapter. Battery tests good with about 6.4v at the terminals. Strictly powered by said battery it appears I'm not getting enough voltage on the 12v line. The floppy drive makes a groaning noise (trying to seek) and the hard drive just clicks with no attempt to spin up. When I plug in the A/C adapter, the floppy drive quiets down and the hard drive attempts to spin up and then fails.

All caps on the logic board have been replaced except for the one at C3 (220uF/25V) since I didn't have one on hand. Would this cause power problems like this? Is there an area on the logic board that I can test the 12v and 5v lines to see if they are working correctly?

Hmm, looks like I may have the same problem as this guy: viewtopic.php?f=10&t=20839