Are you tempted to use your iPhone charger to charge your iPad? Feel free to do so, but only if you have 10 or 15 hours to spare.
We tried using chargers designed for phones on tablets, and vice versa. The phones had no problem drawing juice from the tablet chargers, but the tablets didn't respond well to the phone chargers.
The Samsung Note 10.1 was the worst here--it took an epic 15 hours, 29 minutes to charge using the Samsung Galaxy S III charger. But the iPad wasn't much better; it took over 10 hours to charge with the iPhone 5 charger.
The main problem here was simply the amount of juice available. Whereas the iPad charger delivers a hefty 2100mA of current, the iPhone charger can muster only 1000mA. This makes charging the iPad's massive battery of the iPad rather like carving out the Grand Canyon with a seasonal stream: it works, eventually, but it requires a lot of patience.
Not all USB ports are created equal
When it comes to charging a phone or tablet from a USB port, not all USB ports perform equally well.
The Samsung Galaxy S III we tested took more than 5 hours to charge via the laptops, while the iPhone 5 took between 2 and 3 hours. That's because the iPhone 5 has a smaller battery than the Galaxy S III (1400mAh versus the Samsung's 2100mAh). Windows reported that both devices were drawing 500mA of power while charging.
This situation became more complex with the power-hungry tablets. The iPad took just 6 hours to charge from the MacBook Air's USB port, but it needed more than 25 hours to charge fully when hooked up to the Lenovo ThinkPad's USB port.
That's because Apple phones and tablets can request more power (up to 1100mA) from the USB ports of Apple devices This neat trick only works with Apple products, however: The Samsung Note 10.1 took more than 15 hours to charge from the same USB ports.
USB 2.0 ports on laptops can deliver 500mA (increased to 900mAh for USB 3.0), but only if the device requests it.
Otherwise, they deliver about 100mAh, to keep from overloading the device. The faster-charging feature is available on some recent PCs and is usually referred to as a high-current USB port.
Check your laptop's manual to see which (if any) USB devices offer this feature and how to identify a high-current port.
Sign up for Computerworld eNewsletters.