Several steps can help maximise the service life of a UPS battery and minimise the risk of premature failure.
Importance of battery maintenance, monitoring, and testing A proactive and rigorous preventive maintenance regime is recommended for the UPS system as a whole, but it is particularly important for batteries.
This strategy should start with a proper monitoring regime that detects any issues early enough to enable swift replacement, so they aren’t allowed to develop into a full-scale failure. It is essential to monitor batteries at the individual cell level annually.
Physical tests should cover the inspection of terminals and connections for corrosion and checking batteries for any cracks, leaks, or swelling. Engineers should also tighten intercell connections, where necessary, clean the batteries, and remove any debris.
As well as these basic manual checks, dedicated battery monitoring systems can offer more advanced support. Ensure the monitoring system covers all the parameters recommended by the globally-recognised IEEE 1491 standard, including:
- String and cell float voltages
- String and cell charge/discharge voltages
- AC ripple voltage
- AC ripple current
- String charge current
- String discharge current
- Ambient and cell temperatures
- Cell internal resistance
Along with robust maintenance and monitoring, several tests can determine whether a battery is approaching the end of its life.
Many modern UPS will test their batteries regularly, usually every 24 hours, and will alarm if there are any faults. The test places a load onto the battery set and monitors the discharge. However, this only provides a general indication of the overall battery set, not the individual cells.
Impedance testing is a non-intrusive way of building up a ‘history’ of every battery cell. It should be undertaken annually to track performance over time, making it easier to identify any signs of weakness or deterioration. An AC current is applied to each battery via probes attached to the block terminals, with the impedance measured and recorded in milliohms. This gives a broad indication of the general condition without placing any undue stress on the batteries or requiring them to be taken offline.