It would be nice to be able to power certain household appliances like the coffee maker, for instance, from your car battery. However, this is not possible without some effort, because the car battery provides direct current (DC) while household appliances need alternating current (AC). This means that you have to convert the 12 volts of DC that the battery is providing into 120 volts of AC that the appliances need.
You will have to invest some time and money in order to accomplish this task. You will need some specific equipment that requires installation and it would be useful to know a few things about how the car battery works and stays in place.
First, you have to buy an automotive power inverter that is usually available in auto stores. This inverter will turn the 12 volts of DC into 100-120 volts of AC, which is usually the norm for household appliances to work. You will notice that inverters have a certain power, which is measured in watts. Find out the power of the appliance you want to use and then buy an inverter, which has similar power. If this is not specified on the label, ask the producer or the vendor to figure it out. Similarly, if you do not know the power that your appliance needs, find it out from the producer. When buying the inverter, also buy any other equipment that you might need for installing it.
Read the instructions for installing the inverter and follow them. Make sure you do not miss any step because the inverter might not work.
Test the inverter with a device that requires low power in order to make sure it works.