Lumens Xenon

What rechargeable batteries should i use to power this bulb/lamp?

Hi, i need a really bright light to ride off road at night (between pubs!) There is a 600 lumens torch on ebay but it costs £22 for the postage alone (from Hong Kong) and i am currently very skint. But i have found out that i can buy the bulb on its own http://cgi.ebay.co.uk/Solarforce-L600M-Philip-600-Lumens-Xenon-Bulb-S007_W0QQitemZ280165032170QQihZ018QQcategoryZ117110QQtcZphotoQQcmdZViewItem
When it is in the torch it is powered by 2 X 3.7V 2000mAh Li-ion rechargeable batteries. I dont mind carry the extra weight of heavy batteries as i have a good rucksack that i can wear to spread the load, but what is the cheapest rechargeable battery/batteries that i can get which would be suitable to power this bulb?
Sorry if this is simple stuff to you, but i cant afford to buy this bulb and then blow it and i know zilch about electronics!!
It needs to last for about 1 hour.
Thanks very much for any help that you can give.

The important factor is the voltage. I assume these batteries are in series to give 7.4volts ( that is positive of one to negative of other ) not in parallel which would still be 3.7v ( that is positives together and negatives together ) assuming the former then you have 7.4 volts this can be supplied with 5 x 1.5 volt batteries which should give about 7.4v I think D type would be best they are the largest, and therefore last longer between charges

35W HID Xenon Torch Flashlight 3500 Lumens Spotlight