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Charging The iPhone 4: USB vs. Outlet

July 9, 2010

An interesting article has just appeared on When Will Apple?, in which the charging times of the iPhone 4 via USB and outlet are directly compared in an attempt to find out which is the quickest - and by how much. A series of test conditions were established, and readings of the device were taken every five minutes. The results highlight what we'd expect to hear: charging the iPhone 4 via USB takes longer, but the difference between USB and outlet is a massive thirty minutes - 23% longer to get full charge when charging via USB! You can check out all the information about the test below, including a graph displaying the differences discovered. The conclusion this experiment brings us to is simple: charging via USB is convenient, but if you've got a wall outlet handy then always opt for that. Read on to find out more about the test. Test conditions
  • Started with completely dead iPhone.
  • Wall outlet: standard US 120V / 60HZ.
  • USB charged on late 2008 13" aluminium MacBook.
  • iPhone was checked quickly, 1-2 seconds of screen time, every 5 minutes for its current charge - therefore minimal impact on charge time.
  • iPhone screen kept to a very dim level.
  • Wi-Fi off.
  • iPhone 4 was active on AT&T 3G during charge. Activity on the phone included;
  • Outlet test: 2 texts, 1 phone call (cancelled), 1 voicemail.
  • USB test: 1 text.
These conditions were kept the same for both tests, so any impact they might have had upon the charging time would have been the same for both the USB and outlet tests. Below you can see a graph displaying the results obtained.

So, what do you think? Do you ever charge via USB? Or is it a sync-then-disconnect type affair? Personally, when working I usually keep my iPhone plugged into my Mac just so it's topped up. For overnight charging - or quick, need-power-now charging - I've always opted for a wall outlet. You don't really need a graph to tell you it's much, much faster.

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