Lots of different varieties out there, many badged under different names but still internals. I work as a UPS commissioning engineer so if you want any specific facts etc then I may be able to help
2 companies worth a look are chloride harath and constant power services ltd who service the systems on the site where i work.they are based in hitchin hertfordshire but are nationwide
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc