Just a thought to pass on. I bought one of those cheap cigarette lighter voltmeter plug ins to monitor my battery. Besides the stated inaccuracy of the device, it does not give the voltage at the battery since there is voltage drop in the system. In my case with the battery at rest, the difference in voltage measured at the battery and shown on the plug in voltmeter is 0.36 volts less. So, know what you're reading on one of those gizmos.

 

You will need to put it in the trunk like I did to get better results.

 

Nicely done.