Yamabu, if I have only one strong light it goes on the helmet.
You can carry the 4-cell battery in your pack or jersey pocket.
I posted a link to a source of powerful 2-cell batteries. I prefer to have one of these attached to the back of my helmet. Great price but can be slow shipping. For the price you can get several.
http://www.kaidomain.com/p/S024746.KBP-18650GA2S1P...
You can also buy a GoPro headband and attach the light on the front and the 2-cell on the back with some velcro for a killer trekking light.
For the $, you can get a Yinding as your bar light or backup- it'll work with the same batteries.
Ideal setup for biking is a narrow spot on the helmet and a wider flood beam on the bars.