Or Buy a 24V Red,Green,Yellow or Blue one from RS or Farnell. Wont be as cheap or small as getting a standard LED and adding a resistor. Dont forget that 25mA at 22V is 0.55W so a standard 0.25W one wont do. I usually put to smaller resistors in each wire at the battery that way if either wire is shorted to anything you dont get any smoke.