Takes rechargeable or normal batteries.
With two rechargeable batteries I can get 2 recharges on my Nexus S, which means I can pretty much do anything all day or not have to visit mains for 2-3 days. Got stuck in a departure lounge after a flight mix up and just watched videos for 4 hours and left with a full charge :)
For this price have one with your gear, you are never far from a supply of AA batteries.
Two Minor Cons:
1) As others have said it's a trick to get the case open.
2) The switch is 'off' in the mid position. I've found if I switch it off, I've actually put the torch on. I have unnecessarily illuminated the contents of my rucksack on more than one occasion, so do check!