My sister has a 2009 Honda Pilot that's got some issues with the electrical system.
The battery frequently drains overnight (every other day or so).
When driving a lot (several hours or more) the car will start the next morning. When driving not much (like yesterday about 10 miles) the next day the battery was so dead it couldn't even unlock the car doors. Medium timed drives may or may not start the next day.
They took it to an Autozone and the guy plugged in some type of computer that said it was the alternator. However, we just started it this morning and my voltmeter read 13.5-13.7 volts. It was reading about 13.7 volts for about 10 minutes and then it dropped to about 13.5. Though running the engine steady at 2,000 rpms made the volts stay at a steady 13.7.
They've been having intermittent problems with the air conditioning. At lower speeds it seems to work fine, but at higher speeds it stops blowing cold air. Occasionally when they turn off the AC condenser it will actually sometimes blow colder air. They took it to someone who pulled the dash off and found that the expansion valve(?) was stuck and was causing freezing (literally, ice inside the dash) to occur. They think that problem has kind of gone away since coming to much warmer climate (Arkansas, we've been in the 90ºF mostly), but they weren't sure if that was related to the electric. They were told that alternator problems could cause issues with AC & other things.
Is it likely that the alternator is causing the battery drain? If not, what other things could we check? The battery is 2-3 years old.
No lights are left on at night :)