I totally love my TM-2025RV.
It does so much more than measure voltage and current amp usage.
By placing the shunt on the ground leg, the unit displays charging amps; discharge amps; percent of total battery AH capacity remaining
; voltage measured in 10ths of a volt; and amps in 10ths of an amp (100 milliamp).
Trimetric TM-2025A Battery Monitor System
You will also need to buy the shunt.
Oh, BTW the batteries were being charged off the truck's alternator at the time of the photo.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW