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How is energy conserved in a theoretical circuit where you put a lightbulb and two rechargeable batteries like... (diagram included)

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In the beginning the first battery is fully charged, and the second is fully discharged. As the circuit is connected the discharging battery recharges a dead second battery and light is emitted from the bulb, using up energy. Because the amount of electrode material moved in the batteries is proportional to the current, that also determine the amount of electrochemical potential energy stored. After some amount of discharging the voltages will come to equilibrium with the batteries both half charged. But then you would still have half the chemical potential energy in each = full potential! So you could take one of the batteries and flip it in its place (reverse its polarity so their voltages don't cancel out) and run the lightbulb for as long as you'd have run it with the one battery. See the problem? 1 chemical energy turned into about 1.5 of itself... what did I break? lol