Batteries: Two-6V In Series, or Two-12V In Parallel ???

Digital voltmeters do draw a small current to light the display and run the circuitry in the meter. I haven't measured the current but I fused it at 100ma.

I switched it to turn off the light they put out and even though the current is low, it's a little more current drain when I am off the grid. Maybe it even extends the life of the meters???