There's a selector button on the charger. Yes?
A simple charger is going to control either the current, or the charge voltage.
Think of it this way.
If the charger and the battery are at the same voltage, no electrons are going to move.
To get the battery to charge, it needs to be connected to something with power at higher voltage. The voltage difference is what gets the electrons to move. When they move through the internals of the battery they reverse the chemical reaction and rebuild the charge energy.
We know on most cars the alternator is regulated to provide power from 13.9- 14.9 Volts.
Let just call it 14.5 Volts.
After starting the battery is low and we see on the ammeter that it is getting recharged.
So 14.5 Volts is enough to recharge the battery that might be down to 11.5 Volts.
As the battery charges, its internal voltage comes up. As the voltage comes up, the charge rate comes down. We see that on the ammeter. When the meter shows no charge, the battery is up around 13.4 Volts. This is the surface charge, which is kindof like a buffer.
So when fully charged 1 Volt is not enough difference to get electrons to move.from the alternator through the battery.
If we set a charger to charge at 5 amps, it will increase the voltage as needed to maintain the 5 amps charge rate.
The same is true for any charge rate we select on a manual charger.
There's a photo sequence showing that
here
Its why we shouldn't recharge a drained battery with the alternator.
The voltage difference is high and so the charge rate is high.