Pasdad1 is dead on. The echo charger should be connected fine. It is basically bypassing the isolator if it is working correctly. Having batteries that went to 2 volts means you need to seriously change them out. Especially if you have done it several times. They have been damaged terribly.
Take the echo charger off, replace the batteries, Let your onboard charger bring them up and then run your engine. Only then should you put the echo charger back on.
Myron & Deborah
08 HR Endeavor 40 SKQ
2012 Ford Edge Limited FWD 3.5L
Aluminator tow bar, Demco base plate