I just purchased a light. I considered a light with a removable battery and external charger but decided upon a dedicated bike light with built in charging circuit. I didn't want to bother with taking batteries out of the light to charge them. I also wanted a foolproof design. Lithium batteries have been known to 'vent with flame' when charged improperly. I probably worry too much, but if something can be done wrong, sooner or later I will do it wrong.