Battery went from working fine day after day and then suddenly nearly
dead the next day. Connections, wiring, etc. all checked out OK.
Voltage dropped from 12V to under 6V while trying cranking.
I connected to a trickle charger and in 2 minutes it showed fully
charged. Same symptoms on starting again.
I connected a battery from another car and it started fine. Alternator
was putting out 15V steady.
Took the old battery to a specialty store and it was less than half
capacity. Bought a replacement and installed it. They also checked
alternator & regulator and were fine.
Group 65 battery with 3 yr full replacement warranty was $90, so I took
a chance on that one over the $140+ versions at the chain shops.
No help needed here -- just passing on the info.