The Cateye Reflex has become my favorite rear light for the reasons the OP mentions. It takes two AAA rechargeable batteries that are easily replaceable, but it also contains built-in reflective technology to keep you safe at dark even if your batteries were to die. Add some LED technology to the mix that last between 30 hrs (constant) and 120 hrs (flashing) at a very attractive price, and this rear light is hard to beat. I've had mine for about 4 years. I used it for about 6 months when I first bought mine and then moved on to what I thought were "better" rechargeable lights. I came back to the Reflex about a year ago when I started doing really long brevet rides. I keep them on even at daytime for extra safety due to their long duration. No worries! Highly recommend it!