HHO is a scam, only idiots believe in it. It's a tub of electrolyte with two electrodes in it, you already have six such cells in your 12V lead acid battery, why would you need to put another one in?
The term hydrogen fuel cell has two different meanings that describe two different reactions between electricity and chemical bonds. In a hydrogen fuel cell electric car the hydrogen fuel cell combines hydrogen stored on the vehicle with oxygen in the atmosphere to produce the waste product water and electricity. The electricity is used to power an otherwise electric vehicle. Some batteries may be involved to respond to peaks in power usage. This is the legitimate use of the term. The bad boy cousin usage borrows the legitimacy of the name and applies it to a device used to split water into the components hydrogen and oxygen. The makers propose that the hydrogen and oxygen split in this way can provide more fuel to an internal combustion engine increase the fuel economy. But the reaction does not produce energy in both directions. The fuel cell of the fuel cell electric car produces energy from a chemical reaction. The bad boy cousin requires energy, more energy than is produced when later combining hydrogen and oxygen in the engine. The net contribution of this device to an internal combustion engine is therefore a negative not a positive. It just plays upon the idea of producing energy from water. In many circles this is the description of a scam.
