The Daniell cell has two active electrodes, meaning that both the copper and the zink electrodes participate in the redox reaction. However, in a lemon battery for example, the copper electrode is inert - it doesn't participate in the redox reaction. When is it possible to only have one active electrode? Is it possible to generate electricity by using two inert electrodes?
A non-chemical way to generate electricity using two inert electrodes in salt water is through magnetohydrodynamics. If the salt water moves past the electrodes in a magnetic field, it generates an electric current without consuming the electrodes or electrolyte.
This could make an interesting "magic trick" or puzzle: use a moving magnetic field, e.g. a magnet attached to a motor, in a box below a beaker filled with salt water, and insert two carbon electrodes connected to an AC current meter. Of course, make sure the motor is very quiet.
Technically you could, just place two graphite inert anode in a Zinc Sulfate electrolyte, charge the battery with about 2 volts and you will end up with a Carbon/Zinc rechargeable battery