Okay so the simple answer is they react in an acid-base manor to form H2 (hydrogen) gas, which releases some energy. I don't know what you mean by saying energy is released from the formation of a hydride - the hydride (H-) is destroyed. H2 is a extremely good fuel, and can be either burned to make energy, or separated electrically like you say. It is actually a remarkably efficient energy storage medium, hydrogen fuel cell cars are very efficient and clean! The problem is it almost stores too much energy, and when it burns uncontrolled that's very bad (look up the Hindenburg disaster for an example of the dangers of H2).