What batteries can be charged inside USB rechargeable flashlights?Updated 2 hours ago

Each flashlight can only charge the primary battery type it's designed for. A light that uses and comes with an 18650 battery will charge that 18650 - many of these lights can also run on CR123A batteries as a backup, but can't charge CR123A batteries. Similarly, a light that uses a 14500 battery can only charge that 14500, even if it can also run on standard AA batteries as a backup (the charging circuit isn't designed to charge AA). Some models with a proprietary battery pack (like the ARB-L1 series) can only charge that specific battery, even if the light itself can also run on a standard-sized cell like an 18650.