Duracell Batteries, buy one get one free from Sainsburys. Saw this at Whitechapel, and now online.
Normally, £1 a battery, but now BOGOF so its 50p per battery, so not bad at all!
And if anyone's got those Coupon at Till vouchers, buy about £20 worth, and save more money! (assuming you have that voucher!)
Available online and in store.
Just search online for "Duracell AA" after clicking on the link.