There's a whole class of these cheap, easy to use DC-DC converters to change 12 volts to 24, 24 to 12, 12 to 5, 24 to 5, etc. They are high efficiency. For boats, trucks, military vehicles, appliances, etc. you can get a whole range of converters. This one is a 12-24 volt up converter capable of 5 amps output.
https://www.youtube.com/watch?v=N5GFCy-8DmI
