A better choice would be something like a Xantrex LinkLITE Battery Monitor. This device actually tracks the energy removed from your batteries. At a preset discharge level, an alarm rings. There is also a contact closure that could run to your auto generator start, so it would start and automatically charge the batteries for you.
If you have a Magnum Charger/Inverter, they sell an option to monitor energy use.
Scott & Marcia Hicks
2009 Alpine 40' FDQS 425 ISL