I'll load it up with bleach and do an overnight test as you recommend.
I also found that for some reason the SWG was configured for the wrong cell type. I have a SC-48 and it was configured for a CC-15). It didn't use to be this way so someone must have changed it. Since it takes some effort to do this (have to hold the select button down for 13 seconds to get into the right menu), it probably wasn't one of the kids (meaning the leading culprit is me). I set it back correctly 3 days ago.
But I've yet to see it ever say anything other than "OFF" on the menu since I've been having the problem. When I run a system test, it reports 0V and 8 amps. I have the power level set to 3 (from last year). So it's giving every indication of not turning on, even when I put it into boost mode and spot check throughout the next couple of hours). I inspected the cell itself and the plates are all free and clear of any scaling.