Power Practical's Practical Meter — $24.95
How fast do your iOS mobile devices charge? It can depend. Some are slow and some are fast. Different cables and chargers can make a difference — some can even be dangerous.
This lack of knowledge can be improved with a Power Practical's Practical Meter. It displays the real-time charge rates of any USB device. For example, charging an iPhone with a PC may only get a throughput of 2.5 watts, which is 50 percent of the iPhone's maximum charging speed. A full charge will take 4 hours. However, plug it into a Mac and it now will charge at 1.5-hours, the 5-watt top speed.
I purchased one of these devices in a Kickstarter project and now it's available in retail. It includes the metering dongle and a three-headed USB fast-charge cable.