I bought this battery so I could have a spare to my Olight Seeker 2 Pro. Like the battery that came with the light, it arrived at about 3.58V and took over four hours to fully charge to 4.20V. As with other Olight customized batteries, (rechargeables dedicated to a certain model flashlight) it has to be charged while in the flashlight with the magnetic charging system. It would be nice to be able to charge it outside of the flashlight in an external charger, such as the Nitecore SC4, but it can't be. It wouldn't fit anyway because of the plastic rim around the positive terminal. The battery measures 75.5 mm long. The battery performs as expected and I am happy with the purchase.