Was in my local Poundland today and they had a great deal on Kodak AA batteries - 10 + 1 free for just £1 (link below).
Dunno how good the battery life is, but seems like a very good price regardless. Ended up buying a few packs which I expect will last me ages.
Just gone on their website and it's advertised on there as well. Link here: http://www.poundland.co.uk/product-range/a-z/kodak-aa-batteries/