Deleted a bunch of stuff since I just realized what your real issue is. You're having really bad surges coming down your lines and blowing **** up. So what you need is a surge protector before the UPS. UPS usually has surge protection built in, but its generally pretty weak. APC's manual says not to plug it into a surge protector, but that is because of the extra length of cord for the surge protector, people generally use the cheapest surge protectors they can buy (smaller gauge wire), and chances are people are going to be plugging other stuff into that same surge protector where the power isn't evenly distributed. Once the MOVs go in a cheap surge protector, then its just a power strip.
I looked up the simple 550VA APC UPS and it only has a 365 J surge protection on it. My Tripp Lite double conversion online UPS only has 570 J (not much at all). If you're having heavy surges/lightening then no wonder the APC units are blowing up.
From my limited search there seems to be a couple really good surge protectors/suppressors that you might want to take a look at.
SurgeX XF2 1 left at amazon onsale for $213 and
Brickwall 2 outlet Surge protector for $189. Pretty much stop surges dead in their tracks. Even though they both have two outlets, you would only plug the UPS into it. APC voids warranty for plugging their UPS into a surge protector or surge protector into their UPS. This is mainly to cover their butts since people will do all sorts of dumb things when it comes to electricity. I think they both have a limit of 8A so 960 watts max.
For clean power I'd suggest a double conversion online UPS. Might want to do a quick read of
UPS Wiki Info and
pcguide UPS Info. I got a Tripp Lite su1000xla used off ebay for $200 shipped sometime ago. Normally they go for about $400 and so do the other online UPS, so you're best bet is trying to find a good used one then changing the battery out if its bad. Of course now you're looking at large sums of money, so just stick with your APCs. My Tripp Lite UPS only has a rated 570 J, which is fairly low when you compare it to surge protectors.