Abstract: An accessory device or rechargeable energy pack includes a rechargeable battery or other energy storage that is rechargeable by way of an external source. Energy stored within the accessory device may be used recharge one or more other load devices, such as portable computers, smart phones, or other apparatus. The accessory device may be configured to estimate operating times for such various load devices based on their own respective, stored energy levels, and to communicate those estimates to the load devices or other entities. The accessory device may control an amount of energy delivered to a load device based on estimated energy consumption for a future period of time. Operating times for respective load devices may be increased or managed by way of operations and resources of the accessory device.