I'm not sure line-interactive UPSs will guarantee a change in behavior in and of themselves since they are still stand-by UPS's but instead of cutting over to b

I'm not sure line-interactive UPSs will guarantee a change in behavior in and of themselves since they are still stand-by UPS's but instead of cutting over to battery when in an over or under-voltage situation they attempt to correct it first. For critical loads where I don't want interruption I prefer online or double-conversion UPS's. Basically they have two inverters instead of one. The load runs off of battery constantly on the first inverter, and the second continuously charges the batteries. There is no cut over time when there is mains power interruption since the loads run from batteries. But I hadn't considered this dead battery scenario so that's another thing to add to the checklist of things to ask about. It seems that there should be a bypass mode if there is mains power to supply power to the load too all the time. I've found UPS's to be a mixed blessing - when the power does glitch they can save your bacon but the battery maintenance issue can cause their own outages. If I lived in Florida with their legendary lightning I'd just put up with it but I used to have UPSs on everything and these days I have really dropped down where I have them since we get maybe an outage a year and glitches are equally infrequent too.