I had a battery changed in my Polar watch changed at the Timpkins, Sloan Square store on Kings Rd. Prior to taking the watch to Timpkins it was waterproof, they installed the wrong battery and it was no longer water proof (not even to wash your hands).
I subsequently returned the watch to the manufacturer (who told me that it had the wrong battery in it), Timpkins responded that they weren't prepared to do anything about it (even though i had a 1 year guarantee receipt from them).
I have never experienced such bad customer service. And would strongly recommend people not to use Timpkins.