Ever since the local shop plugged into the OBD port for the state inspection, I'm getting the low battery signal overnight. Could this short plug in have the car thinking it's still diagnosing and running down the battery?

 

Doesn't seem likely, but try disconnecting the battery for a few minutes and reconnecting it to reset. Also, if you have a tender, give it a full run.

 

Plugging into the OBD port for any amount of time can confuse the battery management system. The battery disconnect does not need to be for more than about 15 seconds.

 

It is not only possible, it is what happened. If they did not shut down the program for the OBD II reader before unplugging, that is what happens. Disconnect your battery, wait for a minute, reconnect. Solved. There is a thread on exactly this issue.

 

I told the indie this but was dismissed as not plausible. Thanks gents.

 

Can you just pull one of two battery terminal cables or both? Do you lose any settings for the car.

 

Easiest way is to disconnect the earth lead from where it bolts to the floor of the trunk - a single 14 mm (maybe 13, maybe 15, I forget now!) nut.
You don't need to disconnect both positive and negative/earth, just the earth does the trick and it's much easier than the negative or positive battery terminal lead.
The only settings I have ever lost are the one touch window up/down, easy enough to reset (although for some weird reason in my case the car has to be moving!), and you will lose your Trip A and Trip B figures.

 

Thanks Oz.