A linear voltage regulator is probably not the best option because of the high current requirement (of course that current depends on the device). If you are going to be drawing <1 amp, a linear regulator might be an option.
If you are drawing 20 amps, you will need something like a switching power supply, but be aware that these introduce a lot of noise into your system and aren't appropriate for every application.
If you want an easy solution, put two large diodes(that will handle the current you need) in series in your circuit. 0.7 volt drop on each one = 1.4 volts, and there you have it, 13.6 volts.