Float voltage fluctating periodically on ~5 minute cycle
We have some 70+ APC Smart-UPS SMT1000RM2U units deployed at small wireless repeater sites. They are monitored via AP9630 management cards. Typically, the battery voltage reported via SNMP is 27.0 volts which seems plausible for floating 24 volts of sealed lead acid cells.
Recently I came across one UPS where the reported battery voltage is periodically fluctuating by more than 1 volt on a regular cycle of about 5 minutes. See the graph below.
Any suggestions as to what might be wrong?
It is out-of-warranty. Is there any solution besides replacing and dumping the old one?