I would like to add another large battery capacity ( perhaps Lithium or Lead Carbon ) to an existing Home UPS ( Multiplus 5 kVA 340 AH ) setup. I was considering getting another Multiplus which would manage the new battery and Solar PV inverter and its output would then be AC feed IN to my existing Multiplus effectively replacing the previous Utility grid . Would this work ? Would the downstream ( old ) Multiplus not complain about source impedance perhaps ? What is the maximum source impedance that it will tolerate?