Yes. However they don't use it to both power the car and charge the battery. Kickstarting the engine with a battery is very different from only having a battery and also using that battery to charge itself and the car at the same time.
The original poster was proposing a closed system where you would turn water into hydrogen (a very energy intensive process) and then turn it back into water (an energy releasing process) inside the car to provide all the energy. This is not how physics works. You cannot use your energy source to create more of your energy source without an external energy source. It just doesn't work that way.
They definitely do not work by using a depleted battery to charge a second battery to create energy out of nothing.