Yes, but where does the energy to separate the hydrogen & water come from? I am guessing from the discussion of batteries, that is the source of energy.
Another path they might be using is to make hydrogen by reacting water directly with an active metal. The energy source in this case is the metal, you are recovering a portion of the energy used to refine the metal. For example, you can make hydrogen with freshly powdered aluminum and water. It's been done (but with aluminum wire, not powder)
http://www.keelynet.com/energy/cornish.htm In this case you wind up with aluminum hydroxide as a by-product.
If this works the question has to be not how many miles to the gallon of water, rather how many miles from a pound of Magnesium.
Found this for $46;
"Magnesium Plate .500" x 12" x 12" - AZ31B
AZ31B magnesium alloy machines easily. It is commonly used as an alternative to aluminum alloys due to its high strength to weight ratio. Care must be taken in machining the grade, however, because the chips and powder can be flammable.
And of course it would be good to know the byproduct of the reaction. Just for fun, chemists any thoughts?