For awhile the needle would oscillation between the normal 50-60% position a few degrees after driving a half hour or more with the headlights on. Then I cleaned all the connections in the starting systems from battery terminal to hot connections and grounds, and the problem stopped.
Then last week, I had driven to a store at dusk with the lights on - no problem indicated. I left the lights on for 20 minutes while in the store. Then when I started, the battery needle start oscillating from 50% to 100% regularly, and the battery warning light started blinking off and on.
Car was running fine so I turned off the headlights and just put on the parking lights so I could drive the 2 miles home. After driving about 1/2 mile the oscillating and flashing stopped.
I have tried to duplicate the problem so I could show a mechanic, but all is back to normal for now.
Without knowing anything, I would guest that the computer detected some kind of low voltage and the swinging and flashing was an attention-getter, and not the actual reading.
Any ideas how to troubleshoot this?