At 256K miles I had the battery and open doors, open trunk lights illuminate intermittently. Initially the lights came on for 1/2 mile. 150 miles later it was more like 20 miles on, off for a mile, on for 40 miles, off for 25 miles, on for 10 miles, and then off. A Honda dealer ( after the first 20 miles of battery light being on and 70 miles from home) replaced the battery for $174 and the lights came back on a mile down the road. I managed to get home. With engine running running battery voltage was 14.4 volts. The light stayed off for 30 miles the next day. AutoZone found no diagnostic codes. A mechanic told me that the battery light could be intermittent with a failing alternator. I changed the alternator for $204 ($20 core charge for cracked case). The voltmeter again showed 14.4 volts with engine running. Will the car return to reliability?
14.5 volts is about what I expect when the engine is running. An alternator can work for a while then stop working, so it could have still been bad I suppose. But a bad alternator wouldn’t usually turn on the open-door dashboard light. So that would make me think it wasn’t the alternator, but more likely a corroded connector somewhere between the battery and that dashboard light.
This is not much help of course, sort of like me saying if your home drains were plugged up “I think you’ve got a stoppage somewhere”. True, but doesn’t help.
To solve this, you’d need the help of a mechanic with the car’s schematics in hand to trace it out to find where the problem is. Don’t want to do that? You could try gently jiggling wires under the dashboard, might get lucky.