what are you talking about? i t matters not if the batteries are rechargeable. the voltage across the battery minus the voltage across the LED is the voltage drop across the resistor. divide that voltage drop by the desired current and you get the required resistance.
you don't put LEDs in parallel. you can string them in series and have a single current limiting resistor but you do not put LEDs directly in parallel with one another. since there is not enough headroom for putting the LEDs in series, then each LED needs its own current limiting resistor. with 45 ohms, you 20mA per LED.