Monitoring your battery isn’t just about knowing its voltage, that is a small part of the picture to knowing how much charge your battery has and understanding not only its health but the health of your whole electrical system. Battery voltage isn’t equivalent to the state of charge, it may go up or down as alternator RPM changes and loads are either switched in or out of circuit. Even when the battery is not under load the voltage is not a good indication of charge level. Voltage changes with temperature and even depending on whether it was previously being charged or discharged.
 
A low voltage on your battery might mean your battery is flat, it might also mean you have too many loads attached. and you have better things to do than watch if your battery is charging by watching the voltage go up over time. A good battery monitor will show you the charge and discharge current. Using this extra feature lets you know if current is going into the battery, if your engines are running at high enough RPM to be charging the battery, or if your solar panels are working as well as you hope.
 
We step up a level if the battery monitor has state of charge monitoring. When programmed with the capacity of the battery, will monitor current going into and out of the battery and can report state of charge as a percentage of the total capacity. Now we have the added capability of seeing not only how much current is going out of the battery, but how long before it is at its lowest allowable level with the present load.