This light is 11 watts so on this battery pack it should run just under 3 hours. I did a late night city ride last Friday night and it held strong for the 2 1/2 hours we rode.
Another of my bike lights http://www.instructables.com/ex/i/9129E65EFFBE102880EC001143E7E506/edit.jsp
Step 1: Get the light "bulb"
Step 2: Next we cut off the copper tags
Then I put the screws in that come with the light. They will hold my wires to the bulb. Yeah.. no socket to buy, no soldering or nothn..
Step 3: Little do dads you will need
Conduit Hanger w/speed thread size #0 3/8-1/2 5pk $1.90 HD
Thumb Screw 1/4 " 3pk $1.29 HD
Wing nut #10-24 4pk $1.29 HD
Round head slotted bolt #10-24 x 3/4 4pk $1.29 HD
Lock washers #10 18pcs.
Male/Female RCA cable (cut one side short aprox 3" for the light and The other long for the battery pack)
and a little toggle switch ..you don't really need it but it is nice.