http://www.amazon.com/APC-UPB10-Univ...ref=pd_sim_e_1
I have one of these and it is marvellous
gives me about 6 or 7 hours of ipod function on the ipad, less with video
claims to be able to run an ipod for 10 hours.
I dont know why they are so expensive on Amazon, I managed to get mine from a tech centre in Bogotá for 40 bucks