The ability to replace the battery was a factor that made me decide to go with my current light setup for my commuter which is 2 x Cygolite Expilion 350s. For the rear I use blinkies (a Radbot 1000 and a PB Superflash Turbo) powered by triple A recheargeable batteries. One thing I also realized after using the Cygolites is that I like their regulated feature and also the low battery indicator. The lights don't dim even while in use even when the low battery indicators start to blink.

I usually start charging the lights even before the low battery indicators start blinking to avoid the possibility of deep discharge.