Powering several LEDs from Batteries
Your series resistor(s) should be sized to limit current to their LED (to probably 10-20 mA depending on the LED) and of appropriate wattage to be able to drop the extra voltage without getting too hot. The resistor is what's going to do all the work here. You want it big enough (wattage) that it won't overheat when the battery is at full charge. As the battery discharges the resistor will drop less voltage, until the battery voltage drops close to the LED's working voltage, and the LED's will dim.

Are these LED's used as some type of indicators?