The idea of using the auxiliary battery of lathe is to use the auxiliary battery of 1.5-2 kWh, because there is a 220V jack on the car for fear that the perforation of the car battery will affect the sound insulation of the car. Although the power is not big, it is only 300W W. I think it should be enough. Before leaving, charge the secondary battery with household mains electricity, and then don't stop charging when driving, so it should be enough to cook with a 600W rice cooker and stir-fry with a 1500W electric wok every day.

If you fry two dishes every meal, 1-20 minutes is enough. In this case, whether the secondary battery will lose power or not depends on your power demand. 1500+600=2 100 is 2. 1kw, and the inverter power will reach more than 2.5KW, with 3KW being the best.

If three meals a day are counted as one hour's cooking time,12vx250AH = 3000w =1hour, that is, the battery of 250ah can meet your cooking needs for one day, and you can go back to the hotel to charge it at night. However, it is suggested that it is safer to use high-power electrical appliances above 48V, and you can also cook and stir-fry separately.

Besides, your idea is not to make a hole, so how do you charge while driving? Do I use the 300W socket in the car to charge?

300w divided by 220 v =1.5a.

Charging time =? Calculated by dividing the capacity by the charging current, it takes 250AH to fully charge a 250ah battery with a power supply of 1.5A, which is equal to 166 hours, so you don't know whether the larger charger in your car can bear it or whether it is in danger of overheating.