After extensive research I bought the Tekkeon my power for iPhone 4 and 2 small modules with the thought that I would later buy 2of the more powerful batteries. I later learned that they were not going to make the bigger battery though their website did not indicate that. Bottom line: after 5 weeks I got the message that the “accessory was not supported by iPhone 4″. I called their ( very friendly) customer service and they told me to reset the phone, do a hard reset etc etc and I did. Nothing changed. I called back a day or two later and asked for an exchange or my money back. I was told that since it was 40 days since purchase and not 30, it could not be returned. I tried to argue in a friendly way but nothing in the way of cooperation. Their customer service is friendly, but very poor to say the least. Stay away from Tekkeon myPower for iPhone 4. Get the Ivyskin or the Mophie Juice Pack Plus. Two friends have had great success with them. Any specific questions, email me at jftoal3@gmail.com