Nature has already been there, done that, got the T-shirt.
Electric eels. 500 volts and 1 amp.
The electric eel generates large electric currents by way of a highly
specialized nervous system that has the capacity to synchronize the
activity of disc-shaped, electricity-producing cells packed into a
specialized electric organ. The nervous system does this through a
command nucleus that decides when the electric organ will fire. When
the command is given, a complex array of nerves makes sure that the
thousands of cells activate at once, no matter how far they are from
the command nucleus.
Each electrogenic cell carries a negative charge of a little less than
100 millivolts on its outside compared to its inside. When the command
signal arrives, the nerve terminal releases a minute puff of
acetylcholine, a neurotransmitter. This creates a transient path with
low electrical resistance connecting the inside and the outside of one
side of the cell. Thus, each cell behaves like a battery with the
activated side carrying a negative charge and the opposite side a
As a point of clarification, batteries do NOT 'store electricity'. They store chemicals which, at the point of discharge, go through a chemical process which generates electricity. Capacitors store electricity. Rechargeable batteries use the applied electricity to reverse the chemical process, storing the energy in chemical form, for creating electricity later.