Extend your runtime without plugging in. The ZX20B booster battery enables you to recharge the built-in ZITHION(TM) battery in your RL20RB or RL20R-without going back to the wall. The booster battery simply slides and snaps into place over the top of the built-in battery and begins charging it, increasing the headlamp's total runtime. The booster also features a rear-facing, independently controlled red safety signal that shines in two modes-solid and flashing-to ensure you are visible from behind. When turned off, the safety signal doubles as a reflector. For added versatility, the ZX20B is outfitted with a chip on board (C.O.B.) mini flashlight that shines 200 lumens with a 10 hour run time plus an integrated pocket clip-so that whether you need more power or a second light, you are good to go. Recharge the booster battery via USB-C and monitor progress of the fast charge system using the charge level indicator. Once powered up, the USB-C port on the ZX20B can also be used as a power bank for other devices.