https://www.amazon.com/dp/B07ZPQMLSV?ref=ppx_yo2_dt_b_product_details&th=1
This has been riding in my pocket for a little over a year. It turns on by rotating the front to screw it in a little and the friction is just right - easy enough to do with one hand while holding the keys, but not so easy that it will turn on accidentally. It has two brightness levels, the first is a low light that is enough to illuminate the immediate area but not blind you. The full setting is surprisingly bright, enough to see well 50 yards or more.
It has a rechargeable battery that uses the now-universal micro USB phone charger. The charging jack is accessed by unscrewing the front until it pops forward under light spring pressure. In addition to the jack, there is an LED that goes from red to green when it's fully charged.
Very handy, very compact, about $16 on Amazon. I bought a couple more just to have in reserve in case they stop making them, or add some useless stupid feature like a strobe setting.