12-volt car vacuums are portable devices that run using the cigarette lighter socket of your car. They can only be utilized in a car. Their suction power cannot compare to that of a corded or a lithium-ion battery vac, so they are not suitable for deep clean.
On the bright side, these are small portable machines that are very handy to use if you don’t have access to the main power and you need a small portable device to do some basic cleaning.
They are suitable for spot cleaning and difficult locations. They are reasonably priced and often come with extras. Two popular 12v vac brands are Black & Decker and Vonhaus.