I use the 12v LED's sold on eBay in both 3mm and 5mm with a resistor which drops to around 7-9 volts, I do the same for all my interior lighting powered by a 9v battery. I use both soft white and bright white LED's depending on location and how bright I want the light to be, usually HL and TL bright white and interior lights soft white. Do note here since RailPro light output is only 5v and using these 12v LED's surprising how bright these bulbs are at only 5v being supplied to them. I talked with Don Sweet at RCS of New England and he even suggested using the other power supply on the module which is what your battery power is (14.8v) and with the resistor on the LED you will probably get total brightness and not burn out the LED, but test before you install, you could add another resistor to adjust light output. All being said, LED's are very flexible going down in voltage, but up not so good, they tend to smoke and go puff. I know some who figure this out on paper using all there electronic knowledge, but I'm old world and commonsense works well for me.
trainman