For what it's worth, Jerry Chamkis uses lithium polymers for the internal rechargeable option on the Aerco. He told me that they have a number of advantages (low self-discharge, lightweight, many charge cycles) but are quite particular about charging. They can explode or burst into flames if overcharged and can be damaged by discharge past a certain point. He emphasized that I should only use the charger that was designed to go with the batteries...