APC Smart UPS 1000 - needs new battery (Speldhurst TN3)

I've been using this for a few years (in a home environment), but the battery warning light is now coming on, and I can't justify the £92 replacement cost of a new battery (https://tinyurl.com/4tx7b29c). It's a sophisticated UPS, and would suit anyone who needs some power resilience for a relatively small cost. Replacing the battery is a very straightforward process.
For those that don't know, a UPS like this smoothes out any surges or other inconsistencies in the mains supply and, importantly, in the event of a power cut, will give mains voltage to (say) computer or network equipment for, potentially an hour or two depending on the load.