Batteries and rechargeable cells for lights
The power format governs runtime as much as the LED does. 18650 and 21700 lithium-ion batteries, from 2,600 to 5,000 mAh, power demanding lights and often accept an integrated USB-C port. CR123A lithium batteries maintain voltage in extreme cold and keep for about ten years, which reserves them for lights kept in storage, while AA and AAA can be replaced at any grocery store.
Chemistries, protection, and maintenance
A protected cell integrates a circuit against overcharge, deep discharge, and short circuit; it measures a few millimeters more, worth checking before sliding it into a narrow tube. Low-self-discharge rechargeable NiMH cells suit battery-powered headlamps; alkaline batteries should be removed from a stored device to prevent leaks. The associated models are presented in the lights and portable lighting section.
