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For example, so I can test different USB ports on my computer and powered hubs to see if one charges my iPhone faster than another.
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Since iOS can indicate the charge in percentages, you could simply get a pencil and some graph paper and wake the screen periodically and record the displayed percentages to fit that data to a charging curve.
We have some questions about getting the charge rate programmatically in iTunes, and you could ask if there is an API (private or public) by opening a question on http://stackoverflow.com but for users (as opposed to developers), the answer is no. You can't get a log file of the charge status directly from a computer or the device itself.
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