TT battery

This is a perfect application for the digital voltmeter from Harbor Freight (free or a couple of bucks depending on the promotion). It is small, and amazingly rugged. Plus, if it breaks or you lose it no big deal. I have a more expensive voltmeter at home, but have a Harbor Freight voltmeter in my trailer's storage compartment. Can be used for many situations, including this one.

Click HERE to see what I mean.