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.
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.