10 days ago I bought this imp500 from this online store
http://www.imaxpower.com
So far this battery pack worked really well with my 3G iphone and G1 phone. After fully recharged powerpack, we can use this battery pack to charge up 3G iphone by 4.7 cycles which is pretty much closed to 500%. I did an experiment, if charge iphone from 0% to 100% battery level, if use this powerpack, it will take less than 1.5 hours, if use iphone original AC wall charger, it will also take less than 1.5 hours. So the charging speed is very comparable.
Regarding the charging LED not off after fully charge, I also contacted them and they give me this reply, a very reasonable explanation. They told me this can be fixed very easily. I don't worry about this too much. Here is their reply regarding the LED issue, FYI...
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The reason of LED (3 lights) was kept on after a fully charge up was to remind the user that iphone battery was fully charged. Therefore the current needed for keeping led light on is very small, which is less than 10mA. This current is so small that it can never never damage your 3G iphone. Therefore inside the powerpack, we put an current protection circuit, which will provent any possible current larger than iphone current limit. We have been measured the current 1000 times and it is very stable and safe
In fact, this LED can be automatically turned off if the users prefer it to be off after a fully charging up. Our engineer just need to adjust the LED trigger threshold a little bit to shut LED off after a fully charge up if this user's preference. We will change it next time.
Thanks for your understanding and feedback
http://www.imaxpower.com
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