For those of you with many hungry devices that demand regular sacrifices of 9-volts etc, I have just received my first order from sevendayshop, a fine bunch of chaps out in the channel islands where vat is a seldom heard word. To give you an example of their prices on batteries;

Fujitsu 9-volts are £12.49 for 10, Fujitsu AA's are £7.99 for 40, and Panasonic Lithium Cr123A's are less than £1.50 each. P&P is £1.95 if you don't mind waiting a few days, and they have Duracell, Energiser and various other brands also at silly prices, as well as memory cards and all sorts of electronics.
As 123A's are usually £5-8 each on the high street, this makes a lot of sense to me. All my surefire torches etc are suddenly much more useful, and no more E-blade flat battery misery!