Try to do a search and find out info on my own but I'm illiterate regarding electrical stuff. Will the blue box multi-charger work with the builtin car electrical plug or do I need an inverter? The car plug states 115V AC 150W. The Blue box states Input 100-240V Output 17.5V 4A. Thanks for the help!

Each battery needs 17.5 V, 4A for charging. You can use a car charger that gives you directly 17.5 V, 4A. In this case you don't need DJI charger. If you use 12V to 110V car inverter, then you can plug DJI charger into it to get 17.5V, 4A Choice is yours. You got to be careful while picking the inverter as it should give good AC output.

Remember though. Inverters should have a PURE SINE WAVE. Not square, even a Modified Square is better than a square wave. Inverter Efficiency - Factors Involved. Another important factor involves the wave form and inductive loads (ie an appliance where an electrical coil is involved, which will include anything with a motor). Any waveform that is not a true sine wave (ie is a square, or modified square wave) will be less efficient when powering inductive loads - the appliance may use 20% more power than it would if using a pure sine wave. Together with reducing efficiency, this extra power usage may damage, or shorten the life of the appliance, due to overheating.

Like he said, the answer is No, Volts x Amps = Watts so only 2 out of the 4 ports would work but most likely the blue box would overheat and fry. You're going to need a 300w inverter at least to run it.

I don't think he can do two as efficiencies of DJI charger also play a role which could be for example 60% So to drive 140 W output, we will need 140/0.6= 230W minimum as output of the inverter.