The Kensington portable USB battery pack is now only £7.97 at PCWorld
This isn't available for home delivery but there seems to be plenty of stock available instore, at least in my area
I've used these for a while and have been happy with their performance
These are very lightweight, only 100g, I use mine to power a portable hard drive, which I use to back up memory cards.
It provides a very cheap solution for anyone out there looking for an easy way to backup CF cards on the go, dedicated backup devices are hugely overpriced in my opinion
I paid over £45 for mine a while back so I think these are a steal at £7.97, they currently seem to be available from various online sellers from around the £25 mark
It also comes packaged with various international adapters, which are very handy if you travel around a bit