The PowerVault is a battery that can be used to recharge other portable devices. If the portable device is running low on power, just plug the Power Vault into the portable device and it will rechage the portable device. This comes in 3 sizes small, medium and large. The 2800 mAh (GXPV-2800) is good for cellphone and smart phones, the 4400 mAh is good for items that allow for larger items or multiple charges for smaller items. The 5600 mAh is large enough to power tablet computers and other devices.