Wurm

Good day today my Inverter stop working.When I investigate my primary batery and Secondary batery power switches was off.When I try to swith on the switch on primary spark and trips again Secondary switch on but display on batery  stay off.Inverter also stay off and don't reset or start up.My thoughts was tat my primary batery was busted so I start disconnect the negative batery wires on primary one from Secondary the ather going into Inverter.When I connect the 2 negative wires to only use the Secondary batery it trips.I checked with my multimeter and find that there is a 49.6v current between the batery - and the Inverter- in.Dont think this is normal.With the negative wires still disconnect from primary batery both baterys started up normal.Inverter don't start up at all. What can be the falt pls.