I ride long brevets and I have been very happy with Cygolite Hotshot taillights. I have 3 of them, 50, 100 and 150 for 4 bikes I have. The light does not have a replaceable battery, but it is very reliable and very customizable as far as light patterns and very inexpensive(you can carry the second one, if afraid the battery would run out). I use very low steady light for night riding that seem to last for weeks and does not annoy riders with flashing or too bright lights in rear . During the day I use random very slow flash pattern that also lasts for weeks. On my long distance bike I have two mounted on the seat stays (just in case battery would die on the one), but I never ran out of battery on the first one in one ride.

In my opinion the Hotshot is a much better light than The Supeflash taillight with replaceable batteries that I had prior. Cost of batteries starts to add up after a while and the light leaked water inside, had to be mounted upside-down for the water to drain in rain. The on/off switch also would wear out quickly.


https://cygolite.com/product/hotshot-pro-200c-usb/
https://www.planetbike.com/superflash-bike-tail-light/