USB vs. AC outlet charging on the iPhone 4

The cable also matters. I've a third party cable from my iPhone that is fine for syncing both devices - but must have a higher impedance and doesn't give enough juice to charge the iPad properly.

I bought a few Griffin Power Jolt SE & micro 2.1 amp 12v iPad compatible car adapters for me & wife. The charge the iPhone 4 quick and run the iPad in the back seat just fine.

http://www.griffintechnology.com/products/powerjolt-se-ipad

Until the introduction of the original iPhone, all our chargers (x4) ran off firewire cables. Also connected to iTunes via FW and transfer speeds were great.

These chargers worked very well with iPhone 2G, but the FW cables couldn't be used to talk to iTunes as Apple changed the specs of the 30-pin dock connector. What a bummer!

At least we still have 2 x iPhone2G, iPod-mini and a 10GB iPod which can all still use FW. In fact the latter was supposedly dead, wouldn't respond when the USB cable was used and was going to be disposed-of. I revived and rescued it simply by using the FW cable.

I stopped using my adapter cable for anything but syncing a long time ago. I usually put the iphone in my alarm clock's dock overnight so it is charged in the morning. If I wind up using more of the battery than usual during the day, I'll charge it in the car (if that's where I am) or using the sync cable with the wall outlet plug on the usb end (if I'm at home). Trying to charge using the Mac (even with an external powered USB hub) is too slow.

Related to this issue, I just bought a cheap car cigarette lighter-to-usb adapter and I plug in the dock cable to that. It charges the iPhone 4, but is there any advantage to an "official" iPhone charger over my solution? I have an older Kenwood head unit that read and charged my old 1st-gen iPhone but doesn't charge any of the newer devices. I plan on upgrading to a newer head unit with newer iPod/iPhone charging/playing compatibility and Bluetooth capability soon, so I didn't want to spend a lot of money on a stopgap charger.

What about with ASUS Ai Charger?

I've seen some misinformation in the comments here, so let me explain how the iPhone charges:

The iPhone charges from a voltage of close to 5V. It does not matter what the source of the power is (like the wall or your car's cigarette lighter or a computer). The iPhone accepts 5V and uses that 5V to charge its battery. The iPhone's battery has a nominal voltage around 3.6V, but it actually varies between about 3V when depleted to a maximum of 4.2V. So there is circuitry in the iPhone that essentially converts 5V to whatever voltage at which the battery happens to be at a given time.

Computer USB ports, with the exception of certain ports on MacBooks/Pros/Airs, will provide 5V at up to 500mA to charge an iPhone. Any USB port should be capable of this, as long as it communicates with the iPhone and follows the iPhone's request for high power (meaning up to 500mA instead of just 100mA). Note that low-power USB ports, like the ones on keyboards and monitors, will provide only 100mA. 100mA charges an iPhone very very slowly.

USB ports on some Macs will offer more than 500mA to charge iPhones, iPods, and iPads. I think the limit on these is around 1A. That's why those ports will charge an iPhone more quickly than a run-of-the-mill USB port.

iPhone AC chargers and car chargers will output 5V at up to 1A (1000mA). During certain parts of the iPhone's charge cycle, it will use over 500mA if it detects that it's connected to a 1A charger instead of a normal 500mA charger or USB port. This allows the iPhone to charge more quickly from an AC or car charger that is capable of 1A, like the one that's bundled with the iPhone. You will see only a small difference in charge times between different 1A chargers, as those that output a slightly higher voltage than the others may charge just slightly more quickly. But all these chargers are outputting roughly the same 5V at up to 1A.

Chargers for the iPad are capable of outputting about 2A at 5V. However, iPhones will not use this much power to charge. I don't think iPhones will ever draw more than 1A, because it is dangerous and actually not beneficial to charge a Li-Poly battery at currents higher than its rated capacity in mAh. For example, the iPhone 4's 1420mAh battery should not be charged with a current over 1420mA. Doing some quick math, 1420mA at 3.7V (roughly the average voltage of the battery during the high-current part of the charge cycle) would mean it draws about 1.2A from a 5V charger (assuming some inefficiency in the iPhone's battery charging circuitry). So I do not think that the iPhone will charge any more quickly from an iPad charger than from a 1A iPhone charger. I'd bet that the iPhone still maxes out at 1A even when connected to a 2A iPad charger. And if not, the improvement in charge time would be just a few percent.

I hope this information is helpful, and I don't mean to patronize the people that already know this stuff!

I find I get the "not charging" message when I use an iPhone cable via Mac mini USB port, but not if I swap to the iPad lead. Weird.

I've found I can charge my iPhone in a few minutes if I plug it direct into the mains via a little creative cord splicing. The back bulges a bit but it makes it easier to hold and saves so much time.

Some say it damages the battery but since I swap to the new model every year it's not really a problem.

Might be more difficult with the iPhone 4, not sure if the rear glass panel will bulge quite as well as the plastic ones did.

I'm using 240V 10AMP 50Hz so it might give slightly different time results in your country.

"I doubt a better USB port would get you back that lost 23%."

What is "better" USB port?

Whenwillapple used USB port from 13" MacBook Pro.
Is it not good enough charging Apple device with Apple device?
Do we need iMac or Mac Pro to charge?

Or does your "better" mean "more voltage"? Still, it's a wrong choice of word...