Good afternoon Forum,
After doing some mid-summer maintenance & repairs, my electrical system is now acting up.
I recently replaced an old battery with a fresh 12BS battery, and bought a desulfating charger/maintainer to keep it fresh.
I also added a 12V accessory plug to my dashboard, so I can run a GPS for trips into the "country" with my wife.

Now, after riding it a few times, the system doesn't seem to want to keep the battery charged. I've put it back on the charger, but it doens't want to start.
Thinking the new plug to be the problem, I disconnected it (and the charger "pigtail"), pulled the battery and charged it off the bike. After checking all fuses & connections & reinstalling, it still won't start.
This time, when pulling the battery to charge again, I noticed a hot negative battery terminal.

I'm wondering if this could be the R/R failing (finally after 20K miles), or something more serious? Any help y'all could supply would be greatly appreciated. BTW, I have a quality voltmeter, but haven't begun tearing things down to troubleshoot. I'm hoping some advice from fellow listers might give me a direction in which to begin.