You’re right Robert —Get a good one— it will pay to have a way to recharge a phone or batteries. I’ve been thinking of installing an extra battery in my truck. There’s a module that lets the vehicle charge both batteries but isolates the second battery so you can use the inverter on it but it keeps the main battery seperate so you can always start the car...
In an automobile, in addition to the isolator for the second battery (which is a great route to go!), you can also add a farad capacitor. A lot of stereo enthusiasts utilize them to stabilize power to amplifiers when the draw spikes. A decent capacitor can be found on Amazon for $100 and will assist with peak and start-up load through the inverter. Good luck, you’re on the right track! Always be prepared.