Huh… they work fine for me. You MUST use the come-with charger. They need 5V full USB voltage, NOT 4.2V that’d charge Li cells. The latter almost certainly won’t charge the internal cell worth a damn.
In my Xeno, an alkaleak will gradually dim to the point of being useless. A Tenavolt will maintain full 1.5V brightness (ie, dimmer’n a 14500) right up to the point where it drops dead without warning. Decent runtime, too.