Reduce DC power supply for battery charging
You want to lose about 1.1 to 1.3V from the charger voltage.  A resistor will only work if the current is constant, as you need to use the current to calculate the resistance you need. R = V/I where V is the voltage you want to drop and I is the current.
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A simpler alternative would be two silicon rectifier diodes in series.  Each diode drops about 0.6V, giving 1.2V drop in total.  Make sure you get ones rated for the current you need, perhaps 3A to allow a bit of safety margin.