APC comes to mine as a good UPS battery back-up box, but how big do you really need. At this time, I'm not looking at something to keep it running for hours, just something like maybe a half hour or just to cover you in case you have a power blink, and it won't shut your stove right down. Something long enough to maybe get generator hooked up and or allow it go thru shut down mode. I have a spare APC brand that is a ES550, would this be ok to hook-up to stove to give me a cushion.