In other words:
Be RB the internal resistance of the battery (not constant, beut depending on the charge level!) to be charged, then the current IB has to limited so that
IBIBRB does not exceed a certain value, because much of it will be converted into heat. Some chargers try to measure the temparature to learn whether they are still on the safe side... Some use current pulses to allow a cool-down. This does not change anything to the fact, the the current is limited, and so the voltage to be applied is
UB = RB*IB
There is no further degree of freedom in this process....
The current source of course can be designed to be "most efficient" in providing UB @IB. This will mean that its "natural" internal resistance should be the same as that of the battery to be charged.
I think this is what the OP is talking about...