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I just bought a New Trent IMP99D external battery, to keep my phone alive while gaming during long-haul flights. It has two USB ports to connect to, one which supplies 1 amp at 5 volts, another which supplies 2 amps at 5 volts.

The instruction manual says to connect smartphones to the 1-amp port, and any iPad 2's to the 2-amp port.

Is there any harm, or do I incur any inefficiencies, if I connect my iPhone 4S to the 2-amp port instead of the recommended 1-amp port?

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up vote 2 down vote accepted

When I travel, I only bring my iPad charger and use it interchangeably with my iPhone 4 without noticing any battery life performance and by that extension it should be the same for iPhone 4s.

Apple's website seems to confirm this; For the 10W USB iPad charger - "It also charges iPhone and all iPod models with a dock connector."

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It should be fine, the iPhone has built in safeguards and using the iPad charger wont incur any real damage

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

Welcome to Ask Different! Can you add a citation for this? – Nathan Greenstein Jan 18 '12 at 1:57

It will destroy your battery if you do that for a long time... Mine exploded when I plugged it in after a while of using it! CAUTION!!!!

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This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. – Thecafremo Feb 26 '14 at 8:22

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