What pushes the charge from one terminal to another?

[Markovnikov ya]

in a battery what pushes the charge from one terminal to another at the very first step when both terminals have the same electric potential? how can i start the loop of current?

 

[Naty1]

Hi Markov...
The terminals are not at the same electric potential; there is a potential difference between them, say 12 volts for example in a typical car battery, connected or not.

You 'start a loop of current' by providing a CIRCUIT, an electrical conducting connection exterior to the terminals...those terminals are already 'connected' inside the battery via the electrolyte...an ion [charge] carrying liquid or gel...there is an electo chemical voltage [potential] ready to do work. This means ions [in the electrolyte] are immediately available to flow in the battery and provide power through an external circuit.

In the external circuit, say a copper wire and some electric device like a light or car starter, the moving charges are electrons from the conduction band of the copper atoms. Enough energy must be supplied to free electrons from their loosebinding to individual atoms...easy to do with 'conductors', difficult in 'insulators'.

for more detail, try Wikipedia under 'electrical conductor' and 'conduction band'...

 

[Markovnikov ya]

lets say my battery died. so both terminals are 12V. how can I recreate the potential difference? What do I physically need to do to start the movement of charges? Just apply a current? but then, as I apply current, some charge will move back to the first terminal, and I will not get a high enough potential. How do I build up a high potential difference starting from 0V?

or do I simply need to disconnect the two terminals for the time being, charge one of them, and then connect?

 

[jtbell]

how can I recreate the potential difference?

You need to restore the distribution of chemicals in the battery to what it was when the battery was new. With some types of batteries, you can do this by "running them backwards," that is, by connecting them to a voltage source of opposite polarity (a charging device). With other types of batteries, you can't do this; they're not rechargable and you have to discard them.

 

[Naty1]

lets say my battery died. so both terminals are 12V.

A dead battery will have, perhaps, ZERO volts between terminals; 12 volts BETWEEN TERMINALS is a full charge.
But usually a 'dead 12 volt battery' might read 9 or 10 volts. If it really has no voltage between terminals, likely it has been damaged and perhaps ruined.

The chemical reaction that powers a battery adds electrons at the cathode, while electrons are removed from the anode. these would be available to power a load when a circuit is connected.

To recharge a battery, as already posted, you charge by applying a reverse polarity voltage which is usually about 15 or 20% above the rated voltage of the battery...so a 12 volt car battery, for example, will bulk [maximum] charge around 14.4 volts...and that will be what you read between terminals when the battery is still charging and about fully charged.

You can read more details In Wikipedia...'Battery' or 'battery charger' would be places to start.