The rated voltage is something like 7V-19V, so 20V is probably too much.
If by “on board” you mean in a car, then the car battery should be good enough, with one caveat: You should add protection against “load dumps” that happen in car power systems.
Other batteries that will work fine include any LiPo battery from a RC car or plane, “2S” “3S” or “4S” capacity. (Translates to 7.4V, 11.1V or 14.8V average voltage.)
Note that LiPo batteries are damaged if you over-discharge them, and may catch on fire if charged after being damaged (or if over-charged,) so you also need some kind of over-discharge alarm or other protection device.
Simplest: Buy the following: http://amzn.to/2uETvKp And plug it into the cigarette lighter of your car. Plug the Jetson power adapter into the outlet.
More advanced: Buy some of these: http://amzn.to/2ufWrvP and something like this for charging: http://amzn.to/2uEN4XA and something like this for undervoltage warning: http://amzn.to/2ugeB0P
Most advanced: Get a battery pack, preferrably LiFePO4 because of the long lifetime, with built-in protection circuits: http://www.all-battery.com/ComboTenergyLiFePO4BatteryChargerand12-8V10AhLiFePO4Battery-90593.aspx
Good luck on the project!