What is a battery monitor?

Wayne Dohnal wrote:
I use a Xantrex battery monitor. It has several configurable compensations for things like charge efficiency, Peukert, and temperature. I find it really handy when boondocking to monitor the aH pulled from the battery to know when and how long to run the generator, and when to back off on the usage. Over a long idle period, like when the rig is parked for a month without being plugged it, it horrendously over-estimates how much the battery has discharged. It has an auto-synchronize function to declare 100% SOC based on the voltage and current levels while charging, but that has never worked for me. To re-synchronize I have to look at the parameters and push the button.