I purchased this to replace a dead battery in my wife's dead TomTom One. Installation was tricky - when prizing the back off the TomTom it feels like you could be about to break the body, but it does come apart and there aren't any specific points to release the shell. I also found the existing battery was very securely glued onto the back shell - I removed the sticky stuff so that I could use it on the new battery. I charged it for 24 hours before doing any testing and was relieved to find that it seemed to be fully working.
Subsequently I have not seen my wife. So far I have had postcards from Swindon, Hunstanton, Ramsgate, Wick, Chipping Norton, Stanraer, Fishguard, Penzance, Stonoway, Aberystwyth, Hartlepool and a confused telephone call from Calais - we only have the UK maps.
I can't recommend the new battery highly enough.