I had a b&m battery light for the seatstay, it's a nice light but the mount isn't very good. I suspect the smooth carbon on the chainstay doesn't offer enough grip to keep it from moving around. Luckily it's far enough from my spokes that it hasn't caused problems but this year I'm gonna put a piece of grip tape on the stay to try and hope it stays in place better.
I'm hoping B&M releases something like
the eyro front light with more lux and running time, the eyro is a few years old but I put it on my road bike for riding brevets up to 300k, pretty unlikely to need to run it for more than 5 hours.