What does a battery guard do?

Discharging too deeply can cause permanent damage to your battery.
After too deep a discharge, the battery will no longer be able to reach the same capacity as before the too deep discharge.
To prevent a battery from being discharged too deeply, you can use a battery monitor.
This ensures that when there is a threat of too deep a discharge, the battery’s power output is switched off.
This way, your battery will always remain above the minimum voltage level.
There are also battery watchers that not only switch off the battery’s current flow when undervoltage is imminent, but also give a timely (light) signal when the battery’s minimum voltage level is approached.
This allows you to take timely measures and recharge the battery.
With a battery monitor, you can thus extend the life of the battery.