''What’s so difficult about the question, the cost of charging the battery as a backup, and being paid to discharge a battery into the grid.''
because it's like saying -------------- how much is a hamburger
well - it depends on where you buy it, who you buy it from
you can get a shit one in a very cheap labour country for pennies ------ or you can get one in an upmarket restaurant for a price that will make your eyes water
it all depends on the retailer who you buy your power from and sell your power to
and of course - it depends on atm - if you can. Mostly - you can't. BUT the technology is available
and I suspect that it will come in - and probably sooner than later
