Yes, you are correct, some of these mini-ups keep the lithium cells topped up to 4.2 volts x 24/7, which is bad for longevity. So your tip, to check cells yearly, is a good idea.
IIRC my very first el cheapo 18650 battery backup (DIY- Battery Backup Hubitat- under TEN bucks-NO soldering) killed a Panasonic 18650 in about 2 years by charging it to death.
Download the Hubitat app
