Ouput resistance of a charger
1) The output of the charger is not a simple resistor

2) It doesn't have a defined resistance. A multimeter measures the voltage and current at its terminals, and reports the ratio as resistance. If you have it connected to a simple resistor, that's fine. If you have it connected to a capacitor, the reading will vary over time. If you have it connected to semiconductors, then the ratio will change as the voltage changes. If you have it connected to an active circuit, then things get really complicated.

3) Maybe, maybe not. Because the behaviour is voltage sensitive, you'll need to do the experiment. Connect the battery, and measure the current.