I went through the same thing with a power outage and ran out and bought the battery backups. Good thing I did because it was out for awhile. I just bought cheap batteries for them and they all ran for over 12 hours and still have juice to run some more. I only bought enough to keep 1 stone running in each tank and used gang valves to run them through. I had 5 tank stones running on one battery backup and it did good.