And where to get it for cheap? Mine has died in the cold and only gives me about 5-6 seconds in total of engine turnover before it dies - and that's after a full 12 hour charge.

I'm thinking of either servicing the rear shock or replacing it (a thread about to be made in a moment...) so I may replace it with a thin battery at some point.

I've read to get either a YTX9A-BS or YTX7A-BS, they still the best one for the job? Can't find the 9 on eBay

Get a YTX 9 more powerfull and better.

The 9 is available from Rick Oliver.

Cheers guys, any idea how much?

should be able to get a 9 for £25/£30, worth it for the extra amp hours IMO