I have a M365 battery which looks like one cell is shot. 

It's beyond my limited skills to replace and rebalance the battery - does anyone know if there's a business that fixes these or is someone willing to give it a good for a box of beer or something? (I'm in Hamilton BTW)

Failing that - is there anywhere in NZ that sells affordable replacement batteries? I've found one place that sells them for $250+$15 delivery. There's also Aliexpress but I'm dubious about the quality and stated capacity.