So I work for a company who does a lot of work with power systems for the IT world, and a big part of our business is doing service/repair/batteries on UPS's
We had a great one come in the other day, lets just say for a fairly high profile client, which nearly ended in disaster.
The batteries were only 4 years old (we actually recommend replacing at 3 years) and one of the cells had internally failed, this happens, usually the battery will become swollen and eventually the UPS battery warning light will illuminate (when the battery light is on, usually means you have been unprotected for a while). Anyway the light did come on and the customer decommisioned the UPS to be sent in to us. Now instead of swelling this battery actually busted a seal and a lot of acid had pooled in the battery tray. When lifted out of the rack this acid trickled out of the UPS, and was quickly put on the ground. But it was too late, some of that acid had leaked on to the power module, and tripped the circuitry to turn on the UPS. This internal short started an electrical fire fueled by a bank of batteries.
So luckily this sysadmin had some precautions in place and used the extinguishers outside the server room door. Needless to say this could have been much much worse.
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