The place where I work has a fairly large UPS comprising of rows of sealed lead acid batteries (Haze HZS-7.5HR). The batteries are now 6 years old and are not holding charge very well.
The service technician report states, among other things that ".. the batteries may go into thermal runaway and therefore become a danger to the site."
Is this statement fair, and if so, why would older batteries – which I assume have less energy then new batteries be more likely to suffer from thermal runaway?
Best Answer
I am afraid your service tech is right, older sealed lead acid batteries are more prone to develop thermal runaway. This article summarizes this nicely.
Older batteries do have higher internal impedance, and therefore tend to dissipate more internal heat under the same charge-discharge conditions as new ones. However, if the UPS is well designed and has proper system of sensors, the runaway should never occur, and near-faulty cells should be marked for replacement long before the run-away can occur.