The Whoop 4.0 is recharged via a waterproof, portable battery pack that slides over the top of the Whoop. It uses USB-C charging and takes about 1 hour to fully charge. The charger holds around 5-7 days of charge for the Whoop. Whoop also regularly offers firmware updates to optimize the battery pack, which can be downloaded via Whoop's desktop app and transferred to the battery pack via USB-C connection.