Jimlad, I have a couple of them, the threads are rubbish. That's my bet. Both mine work in one of my FT chargers (I.E. they charge) but not the others ("real" ones from UK vendors) :/ I have been able to force the Bydtechs in at an angle but I wouldn't recommend it unless you don't mind potentially screwing up a charger
e: As RedMogg said above, my FT eGo charger works with the Bydtech batteries
e: As RedMogg said above, my FT eGo charger works with the Bydtech batteries