Fly6 is the only thing I know of that has that kind of battery life. It's rear facing though so in many states won't capture a plate. But it's great for what it is.

I've owned about a dozen cameras. My current one is a Contour Roam3. 3 hour battery life, unfortunately not interchangeable batteries. It'd be awkward but probably possible to power externally.

Getting over 3 hours battery is tough. You'll probably have to settle for interchangeable batteries and carrying a spare.

The Drift Stealth is another decent front cam with a 3 hour battery life, but again, not interchangeable batteries.

The Drift HD and Drift Ghost do have changeable batteries but are $$$.

GoPros have interchangeable batteries but at best 2 hours battery I think. Also they're the most awkward thing ever invented for mounting, and for the money you're not really getting much. If you're going to go with that form factor I'd look at SJCam cameras - look and act exactly the same, cost about 1/2 to 1/3 as much.