Keeppower 21700 5000mAh

The Keeppower 21700 5000mAh carries the reputation the brand built on its 18650 cells over to a larger format: a careful selection of quality cells, paired with a built-in protection circuit, rather than in-house cell manufacturing. The result is a rechargeable lithium-ion cell aimed at demanding users, in powerful flashlights, e-bikes and e-scooters, or home-assembled battery packs.

The 21700 format (0.83 in / 21mm diameter, 2.76 in / 70mm length) is larger than the 18650 whose uses it shares: it allows for higher capacity in a still-reasonable size. On this model, the typical rated capacity is 5000 mAh, with a guaranteed minimum of 4900 mAh, a figure confirmed by independent tests carried out on this range. The nominal voltage is 3.6 to 3.7V, and continuous discharge current can reach 10A depending on the version, enough to power demanding devices. It withstands over 500 charge/discharge cycles.

This cell's main asset remains its protection circuit (PCB), which cuts power on overcharge, deep discharge, over-current or short-circuit. This safety feature, absent from a bare cell, protects both the cell and the device using it, a real argument for everyday use without nasty surprises.

Worth noting before buying: the 21700 format is larger than an 18650 (0.83 x 2.76 in / 21 x 70mm versus 0.71 x 2.56 in / 18 x 65mm), so check that your flashlight, e-bike or battery holder accepts this format. Keeppower also remains a niche brand, rarely found in mainstream retail: it is mainly available from specialist lithium-cell retailers. For anyone after a high-capacity, protected and reliable 21700, it is a solid reference, in line with what the brand already offers in the 18650 format.