+1 on action leds.. good people do deal with.. This one I bought and been using for sometime, will give you 3+ hours on high

http://www.action-led-lights.com/col...rproof-battery

another item which is very nice is the wide angle lense... http://www.action-led-lights.com/col...ide-angle-lens

they also sell a smaller 2 cell battery pack that I use on shorter rides and just put into my stem bag.. I have also recommended this to riders that like using there ms light as a helmet light.. The only issue is burn time about 90 min high w/ p7 and 110 w/ xml model.. If you need longer burn w/ 2 cell pack reduce to medium mode on your light for extra 80-90 min of burn time

http://www.action-led-lights.com/col...rproof-battery