Small and relatively flat, Ventev's Powercell 3000 ($50) is a stone-shaped rechargeable battery pack that can be used with Apple's devices, as well as other USB devices. As the name suggests, there's a 3000mAh cell inside, good for more than one full iPhone recharge. A fold-out micro-USB cable supplies power to non-Apple devices, while detachable included micro-USB and Dock Connector cables can be used with a second device; Lightning users will need…
