Yeah, more s*it to worry about, right Spoke? My Star Union taillight takes a couple of AAs. It was stock with Fättie. It either blinks or it’s solid. There’s no connection to the braking system (which is a little unfortunate). I don’t use rechargeables, so I just replace when the thing goes a bit bonkers as the batts wear down. It’s OK, and it’s better than nothing, but my understanding was that it was one of the knocks on my bike’s model.
I liked the one powered and controlled by the controller as it went solid and bright when braking… But, again, it wasn’t supported by Fättie's stock controller, and I wasn’t able to replace that upgraded controller after Juiced went dark.