For anyone who bought one of these recently and was disappointed to find that the four D cells don't last long, it'll run from 5V and takes somewhere around an amp.
I threw out the battery carrier and wired in a USB lead which fits in the base where the batteries were along with a USB charger when not in use. Then you can use it on the mains, or with a USB 'power bank'.
(My 5300mAH 'power bank' lasted a bit over four hours, which, allowing for it's age and doubtless exaggerated capacity[1] makes an amp sound about right.)
[1] There are loads on ebay claiming 300AH at 5V (theoretical capacity). Well, I suppose if it's 3AH per charge and you can recharge it 1000 times...
Of course, you could just buy a mains one, but where's the fun in that?
Cheers