New Battery, though it would be interesting to find out what was done to
them, ie left discharged for a long time in varying heat and cold conditions
does for them quite quickly.

I think you hit the nail on the head there Brian as to the problem. The charger if that is what you can call it is basically a lead that plugs into a USB supply, the USB plug is somewhat extended and contains a circuit which I presume provides all the €œsmarts€�. As I said before one battery showed 0V and after several hours and still showed the same whilst the second started at 1.5V and showed no further change after several hours. So it looks like it is mend it with new ones just sourcing them seems a problem the original spare was bought from Amazon with the car they are currently shown as unavailable and may or may not be restocked. Bangood do have them on their Chinese website but not on the UK but will not ship from the Chinese site to the UK. Aliexpress have some but from comments from purchasers it seems they are clones and some people have had trouble getting them into the battery compartment which is quite small and a tight fit.

Richard