1. Buy battery from a trusted retailer on Amazon (£10)
2. Buy a kit from Amazon, or as long as you have some tiny Philips screwdrivers for the tiny screws then you ok
3. Most important in terms of 2. is to look for a good suction cup; but definitely much better is to use or borrow someone’s suction cup from a SatNav. This worked a real treat!
4. Use a YouTube clip to take you through, but bear in mind the taking the screen off bit is difficult, but very easy indeed if you use a SatNav suction cup. Also, patience with prizing off the battery. I actually found using a tiny flathead screwdriver better than those plastic things I got with a kit, which broke as too flimsy!