You are right,they fail when most needed!!

This back up runs on water.You run a copper line over to above your sump and conect it to the back up If your main sump fails or the power goes out,the water rises to above the level it would normally pump at,now the back up float rises and trips the back up switch,which lets the water from the copper line drive a turbin which pumps out more water than it takes to run it!! Cheap piece of plastic pump that costs $100,but works well and saved my finished basement. <img src="images/graemlins/ooo.gif" alt="" />