Yes and no. Wirral Spares use a proper battery tester (as oppose to a quick discharge test) which is normally accurate, they are also more than willing to replace one if its duff.
The problem I found is the price was going up and up, I think it was £25 for the one I wanted last time.
For around £30-£40 you can get a NEW Lion battery at Eurocarparts (ECP) when they have their good battery discounts running.
To get best price from ECP, order it online for pickup with whatever discount code is running (currently XMAS75 for 45% off batteries), go into the shop and ask if they can do a better price, sometimes you have to buy something silly like a screewash as well but it gives access to a further discount.
I have bought loads of Lion batteries for numerous people and find them to be excellent batteries, on a par with Bosch Silvers.