Your battery will accept current when the current source has a voltage greater then the battery voltage. The amount of current that flows depends on the circuit resistance. So the current = difference in voltage/circuit resistance. So the answer is it all depends on the voltage that is driving the 25 A source. In general for a good battery life, the charging current should not be above 18/10 = 1.8 A and should be zero when the battery voltage is 14.6 (for a lead-acid car battery, other batteries may be different).
Frank