VRLA battery Thermal runaway possibility

mike95490

well, it's no longer a possibility.
Some industrial gear here at work, had a built in UPS, and the backup batteries (rarely called into play) got cooked somehow. The gear mfg, blames the batteries, and I suppose the battery mfg will blame the charge controller circuit. And the truth lies inbetween.
Mike

redacted account follows:

" We had a case of thermal runaway on a 24 V UPS battery in the data system rack for ### lab. The smell was from gases (hydrogen sulfide along with hydrogen) due to thermal runaway of the cells in the batteries. This sealed lead acid battery was more than 9 years old and got overcharged due to lack of maintenance and expiration of its life. Valve-regulated lead-acid (VRLA) batteries that have aged on a float charge at constant voltage occasionally suffer from thermal runaway. Older batteries tend to have higher float currents and lower thermal conductivity, which moves the thermal boundary lower. It is a good thing we did not have the explosion and/or fire when the safety vent opened releasing the gases. Disconnecting the power saved us from further incident.

Preventive Action:
Run a semi-annual preventive maintenance check on all UPS batteries . The battery manufacturer recommends that batteries be changed every three to five years. The UPS batteries in unused electronic boxes should be relocated back to the air conditioned room, placed on an open shelf, spaced appropriately, and made readily accessible for testing and visual inspection. The environment in that room should prevent the batteries from overheating.

The source was apparently coming from the data system rack for the ###. I noticed the Uninterruptible Power Supply was being charged. When I touched the UPS, it was extremely hot.
The AC power source was then unplugged and all connected hardware was unplugged as well.
The UPS was placed on the bench and the cover was taken off.
Upon visual inspection, it was apparent that the battery was damaged and was collecting large amounts of moisture in the compartments. It was dripping from the top panel.
The pictures were taken after the moisture had been partially dried from the heated panel but you can see how much had collected.
You can also see the discolored wires connecting up to the battery.
The battery seal (or cover) is deformed at the top.
The smell was strong when the panel was opened.
Last service date was 1999. ""