Hello,
I have had an idea but then I watched Iron Man well then it kinda made me realise that it wouldn't work, but anyway tell me wat you think!
Taking a little orb thing that vibrates at high speed to keep the magma(Lava) Hot well taking little anergy to power the vibrations (The meterial would need to be able to hold the magma for a long time as in 25 years or so...) Well you know that you can take heat and transform it into electricity then take the heat waves and turn it into electricity and vola. You wouldn't need a long lasting battery for cars,boats,motor bikes ect... knowing scientist have been trying to have enough power to power a car,boat,motor bikes ect for a long time for like a 10-48 hours.
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If you think it's posible try it 
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If you think it's posible try it :0