"The LEGO® Technic™ Large Hub Battery is a rechargeable lithium-ion battery for use with the Technic Large Hub. This high-capacity, 2,000 mAh battery can be charged while fitted to the hub using a micro USB cable and can also be removed quickly and conveniently without the need for tools.
• High-capacity 2,000 mAh lithium-ion battery for extended use between charges.
• In-situ charging via USB cable.
• Quick, tool-free battery replacement.