Like TheOffice and Jongleur I have a 12V Black and Decker Dust Buster that is going on 20 years old. It still works fine. Unfortunately, the new 12V vacuum cleaners don't work quite as well. They have baffles incorporated which allows them to pick up small liquid spills so they can be labeled "wet or dry". The baffles make cleaning
more difficult and don't really give you much "wet" capacity.
I have had several cordless vacuums over the years and been dissatisfied with all of them. They are convenient for cleaning
up a small mess but lack sufficient battery
life to clean an entire car or boat.
Lithium ion batteries are much better than the old nickel-cadmium rechargeables but they still can't compare with the power available to you from a 100 amp-hour lead acid battery