Installed backup pump per instructions 2 months ago. Tested the backup pump by unplugging main pump and filling sump pit with garden hose. Everything worked fine and gave me a peace of mind that I no longer need to worry about power outages when I'm gone. I went down today to check battery level and that checked okay. It was raining this morning so I had a chance to see main (Zoeller 57) pump cycle on. That's when I notice water shooting out the bottom of the backup pump. It told me the cheap, garbage, mini check that Zoeller uses on their backup pump failed. I should have followed advice and my instincts to remove their check and use a better check in the system.Zoeller should be ashamed that they compromise what would be a good product had they spent a couple bucks more on a better check.I now have to remove the whole system and rebuild it. What a pain.This one major flaw in the design of the pump means that I can't recommend this pump unless you upgrade the check.