Last lot in my small UPS almost caught fire. Nasty smell, chared/melted terminals, distorted cases etc...
Set of 2 12 V 7 Ahr batts for the APC UPS is around £30 delivered from VPS. the "branded" APC replacement are around £60...
Since the near fire incident I've "got at" my UPS and reduced the charging voltage by about a volt (remove an R, fit multiturn pot in it's place) and fitted a fan (remove housing for the SNMP card, fit PC expansion slot extract fan and MIC502 based fan speed controller). The UPS that used to run at "rather warm to hot" is now "slightly cool". I'll be interested to see how long this set of batteries last, around 3 years has been the previous life.
Previous sets have been Yuasa one set Cambden(?).