TL;DR
Battery high temperature accelerates capacity loss. Check the room HVAC, verify individual battery temperatures, and schedule an impedance test to identify weak cells.
What you might see
- battery high-temp alarm on display
- battery room ambient above 25 degrees C
- battery strings showing elevated impedance
- reduced runtime on battery test
Likely causes
HVAC failure in the battery room raising ambient above 25 degrees C
Battery thermal runaway in one or more weak cells
Blocked airflow between battery strings
Charger voltage set too high causing excess gassing and heat
Required tools
- IR thermometer
- Thermometer (ambient)
- UPS battery test kit or impedance tester
- Multimeter rated for battery bus voltage
- PPE: insulated gloves, face shield
Safety first
- UPS battery strings operate at hazardous DC voltage (typically 480 VDC on high-capacity strings). Use insulated tools and PPE at all times.
- Failing VRLA batteries can vent hydrogen gas. Ensure adequate ventilation and prohibit open flames or sparks near the battery room.
- Do not short battery terminals. Internal short can cause an explosion and fire.
Procedure
- 1
Acknowledge the alarm on the UPS display and record the timestamp.
- 2
Measure the battery room ambient temperature with a thermometer. The target is 20 to 25 degrees C for VRLA batteries.[1]
- 3
Check the battery room HVAC supply and return vents for blockage. Verify the unit is running.
- 4
Use an IR thermometer to scan each battery jar. Any cell more than 3 degrees C above the average string temperature is suspect.[1]
- 5
Measure the charger float voltage. Compare against the specification for the installed battery type and temperature.
- 6
If one or more cells are significantly hotter than the rest, isolate that string from the bus and schedule replacement.
- 7
If room temperature is normal and all cells are uniform, log the event and perform a scheduled impedance test within 30 days.
Sources
Eaton Eaton 9395 / 93PM UPS System (Industrial) general technical documentation, Eaton
Eaton 9395 / 93PM UPS general battery maintenance and temperature monitoring procedures (general)
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