I have a 2011 Buick Enclave. The voltmeter in the dash cluster shows about 13.5 volts charging, generally, but occasionally it will drop to around 12. 8 volts, hang there for around a half an hour or so and then move back up to its normal position. It started doing this after a relearn was performed for the engine idle speed. The battery may have been disconnected during the servicing as well (it was a lot of work). The battery is also the OEM unit that came with the car when new. I had the shop do a check on the charging system; they said it showed ok, except for the CCA being about one half its rating and the full charge on the battery was 12.1 volts. I know the on board computer system regulates some of the alternator activities, but any think this is a problem with the alternator itself? Thanks.