Just as an aside I've just seen a very similar and cheaper alternative from Blazewear UK called the Rider, it looks as though it uses the same battery pack as the Keis so I would imagine the Keis bike power lead would fit no problem.
The big bonus is its £75 which includes the basic battery and charger.
I also suffered from the same problem with the controller cable developing a split in cold weather, same temporary repair with self-amalgamating tape and was told by Motohaus to take it back to Bahnstormer for a replacement - which they did no questions asked.
I suspect the vinyl outer casing of the cable must become very brittle at low temperatures (not good for a cold weather device).