[SOLVED] UPS

Solution
Yes it is completely safe to replace the UPS battery, i have done it myself. Just make sure the new replacement battery is the same type as the old battery.
Money-saving tip:
UPS manufacturers do not manufacture the batteries that are supplied in their products; but they frequently put labels on the sides of the batteries in their units, to obscure the industry labeling on the sides of those same batteries.

Example, an APC unit takes a series pair of 12V batteries, as a "Replacement Battery Cartridge". There is a spacer and harness assembly between both batteries, and the whole thing is wrapped in pretty vinyl label stock....it all looks very....pretty, and used to cost $89.99 for the new "Replacement Battery Cartridge".

Removing all those vinyl pretties, revealed that the batteries are standard 7.5Ah 12V batteries, which I was able to replace with better quality shelf units from my local electronics store, for $12.99 per battery.

It isn't much work (far from rocket science) to properly connect the batteries together, slap a bit of packing tape around them, and slide it back into the UPS chassis--and paying $25.98 + tax is a LOT better than paying $89.99 + tax + shipping costs, in my book.