Now, people have claimed on this board that Lithium batteries are much better but I have NOT found any real evidence of that, but every other battery generally has a power in, power out ratio of about 25% i.e. for every FOUR watts you use to charge the Battery, you get one watt out.
Hydrogen Fuel Cells generally provide one watt from every two watt used to charge the Fuel Cell
http://en.wikipedia.org/wiki/Fuel_cellFuel cells was all the rage around 2000, then Lithium batteries came into wide spread use and took the thunder from Fuel Cells. Fuel cells tend to be aimed at larger vehicles, around 2000 for use in electric cars, but then Toyota used regular Lead Acid Batteries for the Prius and that seems to have killed off Fuel Cells for automotive use.
Electric Fly Wheel is 90% efficient, for every 100 watts you put into a Fly Wheel, you get 90 watts out of it.
http://en.wikipedia.org/wiki/Flywheel_energy_storageThe problem with Fly wheels is they are expensive AND dangerous if power gets to low or are involved in an accident where the fly wheel escapes from the device and who knows what damage it will do (Used extensively on spacecraft do to its light weight and efficiently for cost and it being damages are minor concerns in that environment).
The actual most efficient use of electrical power for storage is used in Virgina. Excess electrical power is used to pump water up stream and stored behind a dam, when additional power is needed, the dam is opened and used to generate Electrical power. Hydroelectric dams are the fastest and most efficient method to get more power on the grid, thus tends to be kept in reserve till all other sources are in full use. Plans have been made to expand this type of "Electrical" Storage, for its costs are much lower then Fuel Cells or Fly wheels.
Sorry, unless you are looking at Lithium, Fuel Cells, Fly Wheels, or water storage, the energy savings is NOT there and this article does NOT mention the type of "Battery" and the 90% efficiency mentioned int he article would imply a Fly Wheel NOT a true Battery. Sounds like wishful thinking more then a real plan.