I recently got a Rock Bros 850lm w/10000 amp hour battery that has a daytime flash option (which I use a lot) and it can also serve as a power bank for any USB devices, IE; phone. It is more than bright enough for night riding along with my helmet spot light which I thoroughly enjoy doing. Lots of wildlife to be seen at night when riding an almost silent vehicle,

Had my cateye front light stolen while out shopping and was in the market for a new light.
Ordered one of these Rockbros 850lm for £16.36, too good to miss!

You won't regret it. I've had mine for almost a year now and it's still working like new after many hours of use and abuse in the elements. For a daytime flashing light it's a real attention getter.

I hope that 10,000 amp hour battery light was a typo as anything with that large a battery would weigh as much as your bike. 850 lumens is easily achieved with a CREE XML-T6 LED which is common in some lights and flashlights (I own several). 1000 mAh batteries are also common but if you can find a light that uses the 18650 Li-ion battery and allows you to switch batteries easily, you might do well using one of the better Japanese batteries like Sanyo or Panasonic which are available in 3,400 mAh capacities. That will give you far more runtime between charges than 1000 mAh for the same lumen output.

It's not a typo. It also has a USB port for running accessories out of it. MY phone has a 5000mAh battery and I use it for my bike computer. With screen on and a bunch of other BT apps running, it consumes about 6% battery life per hour. The light and the phone are heavy by many rider's standards, but they work for me.

You wrote 10,000 amp hours when you meant 10,000 milliamp hours. That little m is significant.

Yeah, that went right over my head. Good catch