What sort of LED's are those?
Most LED's drop no more than 2-3.5 volts across them, depending on colour and type.
Be aware that a freshly charged 12 volt battery can give over 14 volts. If you're only driving a few low wattage LED's why not just wire them into the 5 volt supply from your receiver, that way the voltage is regulated.
Subculture,
The spec's of the LED's will state the forward voltage, and the recommended current eg super bright Led typically 3.6v current 20mA above 30mA can kill the led.
The resistors function is to limit the current drawn to within acceptable limits, connecting directly to the 4.8v - 6v Rx pack there is nothing to limit the current
allowing the Led to draw whatever current it wants, at best this will shorten the life of the Led at worst it will let the smoke escape from the Led.
The Maths to work the restor valuu is
Battery volts minus Vf divided by current eg; 12v - 3.6v = 8.4vdivided by .02A = 420 ohms the nearest resistor value would be 390 ohms or on the conservative side 470 ohms.
Damien.