Richard Andrew x64 wrote:

You're forgetting the third and most common form of lead acid battery, the flooded lead acid battery.

Flooded lead acid batteries must NOT be used in office UPC-backups. During last part of charging they vent oxygen and hydrogen in a perfect explosive ratio. That is why one has to periodically add water - to replace the water that was decomposed. They can only be used in a ventilated compartment. Sealed lead acid batteries do not vent explosive gasses, and are OK for indoor use.

FG Fletcher