I've owned a set of the eBay/Chinese CREE lamps with the separate battery pack. While they were quite bright, the battery didn't last very long, requiring a charge twice a day (once at work and once at home). That in itself was a PITA, but then there was the charging wire that failed which required minor surgical splicing, and then the cable from the battery failed, and again, more surgery. The mounting was also a hassle. In the end I just gave up, or rather, it gave up.

I'm currently running two 'self-contained' units. One requires charging once a day as I run that one at full power. The other at night time flash, and then day time flash. Much simpler.

In terms of how much power you need, more is better.