Battery system monitors always monitor your battery system and give you a pretty good idea about the condition of battery condition. They also keep a record of battery backup system in amperes and volts i.e. what you are using and generating.
They keep track of the total amp-hours into and out of the batteries, and the battery state of charge, and other information. They can be very useful for medium to large battery backup systems for tracking exactly what your system is doing with various charging sources.