I currently own the New Trent iTorch IMP52D powerpak rechargeable external battery.  I have owned the product about two weeks now and have had the opportunity to use it 2 times.  I travel just enough that an added charge will make life easier when at the airport or away from the office / car long enough that I don't have any other charging options.  The IMP52D adequately charged my iPhone 4s after a day on the road.  The initial charge took approximately 5 hours.  The iTorch seems to recharge the battery at a similar rate to that of a standard wall charger.  I started the recharge process at 25% battery life.  Following the recharge to 100% battery life, the battery indicator showed 2 bars or half life remaining.