Efest IMR26650 4200mAh

The Efest IMR26650-4200 is a lithium-ion cell in the 26650 format (26.5 x 66.4mm), the widest of the common cylindrical formats, built to combine high capacity with strong discharge. With 4200mAh and a 35A continuous current (up to 50A pulse according to Efest), it targets very powerful torches, DIY battery packs needing high capacity per cell, and electronics projects that call for a large energy reserve in a single cylindrical cell rather than an assembly of several 18650s.

Supplied as an unprotected Flat Top, with a flat positive terminal, it weighs 88.4g for dimensions of 26.5 x 66.4mm. This is a less common format than 18650 or 21700, reserved for devices specifically designed to take it: most high-end wide-body torches and certain custom packs. Always check your device's compatibility before buying, since 26650 is not interchangeable with narrower formats, and most standard 18650 or 21700 chargers will not accommodate its extra length and diameter without an adapter sled.

On the electrical side, the nominal voltage is 3.6 to 3.7V, the maximum charge voltage 4.2V and the discharge cutoff voltage about 2.5V. The IMR chemistry Efest uses favours thermal stability and the ability to deliver high current without runaway, a sensible choice for a cell of this size expected to work continuously at 35A.

Efest enjoys a solid reputation among bare lithium cell users, with good consistency from one cell to the next, a decisive factor for anyone assembling multiple cells in the same pack. As with any cell lacking a built-in protection circuit, a charger dedicated to 3.7V lithium cells and a few handling precautions (a carry case, no short circuits, no discharging below the minimum voltage) remain essential. For devices that accept it, the IMR26650-4200 is a dependable choice at the high end of 26650, whether you are rebuilding a large searchlight, powering a DIY flashlight build, or simply after a single high-capacity cell instead of stacking two smaller ones.