The dreaded dead battery is a constant First World worry these days, but a portable solution could soon be at hand.
The Ampware team has created the new 'Crankcase' - a phone case with a built-in battery and, crucially, an integrated hand-crank power generator. Using efficient, powerful dynamos, it offers a seriously impressive rate of electrical power generation for the effort you put in.
They claim that one minute's crank time can charge a phone for 40 minutes, and just five minutes' will give you an extra three hours of juice.
In addition, using a cable and its USB port, it can be used to power any device; for example, five minutes' cranking will power a tablet for 90 minutes.
As if this wasn't enough, its crank arm can be used as a stand for your phone.
Currently available for iPhone 5, 5S and 6 (with others in development), they're looking to raise $50,000 (£34,000) on Indiegogo - they currently stand at a tenth of that at the time of writing.