Buy a Mophie perhaps? This is what I use for my iPhone when flying with iGlide. The Mophie is a $100 "battery case" that provides roughly 3500 mAh of additional battery capacity (120% additional). With a Mophie, there is no need for wires or a separate portable battery in the cockpit. The mophie case is only slightly larger than a normal case. The Mophie case setup will run an iPhone running iGlide all day (8 hours plus). Far longer if one does not leave the screen on constantly. Also, the Mophie charges from the same single USB wire at night. No need to charge two batteries separately (two wires and charging adapters). No more forgetting to charge the spare battery. Just a thought. www.mophie.com