Apple’s iPad Power Needs Cause Confusion

Judging from recurring complaints over the weekend, perhaps the least intuitive part of the iPad is the way it recharges its battery.

The iPad charges just fine with its included 10 watt power outlet and cable. But numerous iPad customers have complained that their computer’s USB port was failing to charge the iPad, as the battery status read “Not charging.” Apple’s support site states that only “high-power USB 2.0 ports,” such as those included with recent Macs, can charge the iPad.

It turns out that’s not completely true.

Apple’s support site creates a bit of confusion. It reads, “Some USB 2.0 ports and accessories do not provide enough power to charge iPad. When this occurs the message ‘Not Charging’ appears in the status bar next to the battery icon.” That leads you to believe older USB ports can’t charge the iPad at all.

However, farther down the support document, Apple says that lower-power USB ports can charge the iPad — but only when the device is asleep.

“When attached to a computer via a standard USB port (most PCs or older Mac computers) iPad will charge, but only when it’s in sleep mode,” Apple says in the iPad support document.

In other words, some USB ports on older machines can charge your iPad while it’s asleep, but the issue is your iPad can’t tell you, because it can’t charge when the screen is on.

Apple’s support bulletin also clarifies a few tidbits about charging behavior. If you use your iPhone adapter to charge the iPad, it will charge, but more slowly than it would with the iPad’s charger, a fact confirmed by Gadget Lab tests.

And of course, charging with any computer’s USB port (whether it’s high-power or low-power) will be slower than charging with the iPad’s own charger, according to Apple. Also, when charging through a computer USB port, the computer must be powered on — not asleep or shut down.

The USB Implementers Forum ran a full array of tests on the iPad to confirm the tablet’s USB-charging behavior. The organization said that despite some consumer confusion, the iPad behaves very well. The iPad conforms to newer USB charging specifications (Battery Charging v1.1) to ensure that it draws power intelligently based on the amount of power available from any source, the organization explained.

Older, USB 2.0 ports deliver 0.5 amp, which is only enough to charge the iPad when it’s off. Newer machines that feature USB ports conforming to Battery Charging v1.1 standards, and the iPad’s own power outlet, have enough power that the iPad can draw the full 1.5 amps it needs to recharge the battery while it’s running, according to the USB Implementers Forum.

“The good news for consumers is that because it’s conforming to these specifications you’re not going to be at Starbucks and have it suddenly draw a ton of power,” a USB Implementers Forum spokesman said. “It knows how much power is available to it, and based on the power that’s available to it it chooses to behave in a couple of different ways