Demon saddles are awesome. 35C, plenty of punch. runtime around 10 mins. Come with balance lead etc.
http://demonpowerproducts.co.uk/prod...oducts_id=4256
same dimensions as a saddle NiMH, but you may need to modify the battery strap if it has any curves to fit the old cells. If it's a flat strap then they should drop straight in.