Recommendations on quality parts

Currently having issues trying to get parts for iphones 5, 5c and 5s. I have had a solid 6 months of ebay parts with minimal problems. Batteries are a real problem at the moment, every bunch I get my hands on seem to be playing up. I buy broken iphones, fix them and then sell them on. Looking for recommendations on suppliers here in the UK. Ifixit have a strong following but 17 pounds for just a battery replacement is quite steep in my opinion.

Also might throw another question in here.

Does anyone know where to have logic boards looked at and fixed here in the UK, have quite a few laying around that may be easy fixes for someone who knows what they are doing

Cheers