I have a smart ups backup running on my sump. It is supposed to last 8 hours and when that runs out I have a generator I can hook it up to. This is a nowhere near cheap decision though. The smart ups cost me $1800. Only reason I got it was because I know they are reliable as that's what I use for backup on a data network running for a whole town.
Power was once out on my tank for several day prior to the backup and there were no issues. This was also prior to my sump installed.