The full size version of the teardown video including dremeling the case open and more discussion about the construction.

These batteries use a lithium cell and buck converter to give out a steady 1.5V for most of their discharge, dropping deliberately to around 1V at the end to trigger battery warning systems.
They are the equivalent to a 2000mAh rechargeable AA cell and can supply up to 2A, although they do get hot at high current and may cut in and out thermally.

They seem to charge at 5V via the same contacts.

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