Unless the boat is cruising and a sophisticated battery management system is in place, batteries are slowly draining. Which is fine as long they don't drain too much. Sentinel is monitoring the batteries all the time and alerts the user when dangerous levels are in sight. Besides alerting the boat owner, Sentinel can also:
Battery status vs. Battery Health: Sentinel Boat Monitor can do much more than just measure voltage. With an optional Sentinel Battery Sensor it can calculate State of Health and report State of Charge instead of voltage. Battery sensor can be easily retrofitted since it connects wirelessly to the Boat Monitor unit.