UPS Batteries Swell – Why?

UPS batteries swell for a number of reasons.

Sealed lead acid batteries (VRLA) typically used in UPS can swell as they are manufactured in such a way to allow absorption of gasses released during the chemical process inside the battery.In other words, the gases caused by the chemical reaction taking place inside the battery due to age or chemical breakdown and can’t get out. Hence the battery begins to swell gently to begin with and thereafter blows up like a balloon.

The positive and negative plates are packed very close together with only the thickness of the divider separating them meaning there is very little extra space inside the battery. When the cell plates expand, it exerts pressure on the inside walls of the battery. This situation can cause the battery case to swell resulting in possible splits and cracks at various points of the battery. These should be visible long before the battery becomes severely mis shaped.

The main cause for expansion is battery overcharging although it can also happen due to shorting of the terminals of the battery. Both these situations results in heating up of the cell plates inside the battery. The lead of the cell plates has a high expansion rate when heated.

How to Avoid Battery Swelling?

Overcharging or short-circuiting of the battery is the only reason for swelling up of the lead acid battery. The problem is not inherent in the battery itself. In order to avoid swelling up of the battery you need to tackle the underlying cause of the problem.

Modern UPS have intelligent battery chargers that avoid overcharging but a faulty battery charger can easily lead to the batteries swelling.

What to check?

Prior to the swelling up of the lead acid battery, you may sense an ‘eggy’ smell which indicates acid could be leaking from a split battery.

Also check that the battery environment hasn’t or isn’t over temperature – ambient 22C

A faulty battery charger can easily lead to the batteries swelling. Check it’s operating correctly

Check the battery terminals aren’t ‘furring’ up – Keep them clean

Any other concerns?
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