I've never rma'd any ups.....just chuck it and get a new one. Then again, i have never had one that was worth enough to rma that died before the warranty was up. No Tripp-lie or Smart power systems stuff in UK? That sucks, they both make nice power protection stuff.
Well, i have never had an expensive one die before its warranty was up.......I've had it happen to MANY cheapo ones, but who cares about them. Time costs on it being down while being rma'd was not worth the 70-80 dollars a new cheap one costs. I don't like to use cheap ones, and since i have been using nice ones, they don't die before the warranty is up. Every now and then you have a battery fail, but just pop a new one in and get it up and running.
I use two CyberPower CP1500PFCLCD units, one for my gaming rig and one for my workstation / computing rig. They're almost a necessity since my area suffers from frequent black/brown-outs, plus I always keep my rigs on and working. They also provide some protection from surges - during a lightning storm one of my rigs was hit with a surge while plugged in directly into the wall (thankfully it only took out the PSU, but it scared the crap out of me).
I've had my CP1350PFCLCD for almost 7 years..... I had to replace the battery a couple months ago. A good, high quality UPS, will easily outlast it's warranty. The warranty on my unit was only 3 years. Even the battery lasted beyond that warranty. I'm actually considering ordering a second unit from CyberPower because of how well this one has held up.....