Halfrauds are there to make money so there suggestion is typical of a shop who operate in the world of throw away consumer goods, it doesn't have skilled staff to carry out simple bike repairs, a lot of us on here would put them to shame and p**s all ove rthere so called bike mechanic experts.
Any hub bike out of warranty that needs repair cna be done so often for not too much money. Rip out the crappy speed control often from Lishui brand or a no name brand wher one simply can't buy the spares , fit a KT system and one is likely away and gone if the hub has no Hall issues.
Battery wise any generic battery from ebay can be used at a cost of < £200 and far cheaper then the expensive in shop offers from Halfrauds and the like.