Klarus 21GT-50 5000mAh

The Klarus 21GT-50 is a rechargeable lithium-ion battery in the 21700 format, the high-capacity size that powers the most energy-hungry flashlights and devices. Klarus has matched it to its most powerful models, such as the XT21X Pro or the G15, while keeping it compatible with most devices that accept a protected 21700 cell.

Its rated capacity is 5000mAh, or 18Wh of on-board energy at a nominal voltage of 3.6V. Continuous discharge current reaches 15A, enough to power very high-output torches and devices with high instantaneous draw without flinching. The cell has a built-in protection circuit that cuts off automatically at 4.2V on full charge and around 2.75V on low discharge, on top of short-circuit and overheat protection. Klarus rates it for 500+ charge cycles before any noticeable capacity loss, and an operating range of -10 °C to 60 °C.

Supplied in Button Top format, it measures 75 x 21.5mm for 72g, dimensions worth checking if your torch or charger is machined tight for a bare cell: like any protected cell, it's slightly longer and heavier than a bare 21700. It carries CE and RoHS certification, with end-of-life recycling markings printed directly on the label. The extra size over an 18650 also means more usable energy per swap, useful for search lights, headlamps and any 21700 device pushed hard for long stretches.

As with almost every flashlight brand (Fenix, Nitecore, Keeppower...), Klarus doesn't manufacture the lithium cell core in-house, but sources a professional-grade 21700 cell and adds its own protection circuit, labelling and quality control. This standard industry practice takes nothing away from the reliability of the finished product. For a high-end Klarus torch or any current-hungry 21700 device, the 21GT-50 is a consistent choice with no nasty surprises.