Your car electrical system operates on 12-volts like these batteries. When the battery in the portable power unit runs down, it has a cord to plug it into the cigarette lighter socket. It recharges while you drive. Most inverters have two standard wall-type outlets and will handle 300 watts. For simplicity, select a model that has some type of built-in charge indicator so that you know when it is running down.
Some units use a series of indicator lights and others use an actual meter.
Even if you do not get the portable power pack, a plug-in inverter is a great item to have. Plug it into your car's cigarette lighter and it is like being at home. It will power most 115-volt household devices. Update Bulletin No. All the brands that you find at most hardware stores are similar with a similar size tube.