Off-grid charging setups typically combine a portable power station (a large battery with built-in inverter and charge controller) with solar input, sized to the actual daily energy use of the devices being charged rather than worst-case capacity.
Practical note
Off-grid and RV charging systems are more forgiving of imperfect setups than people expect — the main failure mode is undersizing the battery bank or solar input relative to actual daily use, not choosing the wrong charger.