We’ve owned a lot of UPS units over the years, and while their electronics do occasionally fail, more often than not, we’ve found reasonably priced and easy to find battery replacement puts them right back in service.
The batteries are typically easy to replace (consumer friendly) and once you’ve got the old battery out, it is simply a matter of matching its dimensions and capacity specs to a replacement.
However, unless the existing battery is a lithium ion battery, don’t be tempted to replace the OEM battery with other than the original lead acid battery. The voltage profiles expected by the electronics might not be smart enough to match a different battery chemistry.
Same experience. I’ve had multiple APC models (including a Smart-UPS) electronics fail, and all APC would do is offering me a discount code on their store, which charged way more than VARs. Also, APC batteries had a tendency to swell up making replacement really difficult. I worked in a lab at IBM where battery replacement toolkit included screwdrivers and Astroglide because it was such a common issue. APC, never again.
I now have three to four Cyber Powers and they are all reliable, and battery replacement is a cinch. I’m a loyal customer.