There are few things more useless than a portable device with a dead battery, but come this fall a new device called BatteryBox will go a long way toward fixing this problem.

BatteryBox is a external battery that can charge any USB chargeable device but it's primarily intended to work with the Macbook Air and Macbook Pro. It is available now for pre-order at $139 direct from the company. Shipments are expected to begin this fall.

The BatteryBox is about the size of a portable hard drive, but inside is a 50Whr lithium ion battery capable of powering a Macbook Air for 12 hours, a Macbook Pro for 6 hours or eight iPhones. And to give an idea on battery life for those in the Android community, the battery holds 6.25 full charges for the Nexus 4 and five full charges for the Samsung Galaxy S3.

The BatteryBox itself needs 4.5 hours to reach 80 percent of its full charge and 9 hours to be fully charged, all through its micro USB charger cable.

BatteryBox is not just a battery that supplies power, it also is a battery management system, the company said. It uses what the company calls BatteryOS, was developed by a company called Gbatteries. This software controls how the lithium ion battery in the BatteryBox operates enabling it to have a higher capacity and not degrade over time. The claim is a BatteryBox will have 3,000 full charge and discharge cycles and retain 96 percent of its capacity, even after five years.

In addition, BatteryOS also works to extend the life of the mobile device's battery. Instead of simply passing power to the device's battery, BatterOS bypasses it and directly charges the unit. This lowers the number of charge-discharge cycles of the internal battery. Although this only works when the device uses the normal charge port, not the USB port.

The BatteryBox is 0.98-inches high by 2.63-inches wide by 3.55-inches long. It weighs in at 8.81 ounces and is compatible with any Macbook with a MagSafe2 connector or any USB device.