Thanks for all the replies.
The Lazada link from Crossy was just the kind of thing I was looking at yesterday, but when I asked the Thai vendors, they seemed to think it would not be good enough.
Possibly something lost in the translation.
The two pin plug and cable that runs to the charger are just like any other standard Thai electrical appliance. So, I thought anything similar to extend it would be ok.
I would be grateful if someone could just clarify that I do not need a heavy duty cable.