I recently bought this product to use when I go camping and need to keep my cell phone as well as my daughters Ipod charged. I tested it on a Motorola Droid X smart phone and here are my results: From 5% battery life, two Duracell batteries brought my phone to 40% in about two and a half hours and the batteries were dead. I also tried two Energizer Lithium batteries and those gave me a full charge from 5% in the same time frame and were dead. So in conclusion: The product works, but you'll need to pony up the money for lithium batteries if you want it to work well, or spend half the day charging stuff with conventional batteries.