Your 12VDC Battery
OR, Purchase one of those multi use battery
boxes that has an air compressor and tire inflation hose, USB charger, Inverter and best of all a 12VDC cigarette lighter receptacle and Jumper Cables and just plug your 12VDC cable directly into it.
I dont know how may times one of these has come in handy at starting a vehicle or airing up a tire.
Your money will not be wasted.