ChugPlug External Battery Pack for MacBook Air and MacBook Pro $40 shipped (Orig. $130) - 9to5Toys
Lenmar CHUGPLUG PPWMB65 - External battery pack - AC 100-240 V - 60 Watt - 1 x lithium polymer 4000 mAh - white - for Apple MacBook Air (11.6 in, 13.3 in); MacBook Pro (13.3 in, 15.4 in) - Walmart.com - Walmart.com
Sanho Extends MacBook Battery Life Up to 32 Hours with HyperMac | TechPowerUp