A good battery monitoring system should not discharge the UPS batteries, it should only observe the battery, without affecting it in any way. The battery monitoring system should not apply any load to the battery, in the way that is done in so-called battery control systems – Battery Management System (BMS). The battery monitoring system should not inject any current, AC or DC, into the battery, or send any commands to the UPS to initiate a test procedure. It should monitor all parameters of the battery at full speed and record the results from any power outage or battery test.
A battery monitoring system must use a protective resistor. In a room full of batteries the environment is corrosive. Sooner or later this will affect connecting cables. It should never be hazardous to touch any part of the system. There is always a risk that a cable is touched by a closing link with a different potential. With the protective resistor there is no hazard. Without a protective resistor a short-circuit will burn the cable. This could start the automatic fire-control system. Or, worst case scenario, this could lead to an explosion.
Out of all the requirements one can have on a battery monitoring system the protective resistor has to be number one. After all, it is far more important that the system is safe than anything else. The battery monitoring system is a secondary function which should not jeopardize the battery’s primary function or safety.