how to disconnect battery charger on Magnetec converter ?

There is a myth on this forum that the old Magnetec converter chargers are battery boilers. Check the out put of your charger is it 13.6 volts or lower? My 20 year old Magnetec charges at 13.2 volts. I don't know how 13.6 v or lower can boil the batteries. Having said that I use a 40 amp B&D portable charger to charge the batteries after I dry camp, remove the cables and let the 5 amp Magnetec float charge the batteries for several days then use the battery disconnect if I won't be using the MH for a while. These chargers can fail that is why I say check the out put first if it is 14 volts or more then just use the disconnect switch after it is charged and unplug from shore power.

It depends on the design of your camper. On my 2000 Roadtrek there's a 15A breaker called "Battery charger". By tripping it, you not only disable the battery charger, but also the 12v converter.

While on shore power, the convert actually runs all your 12 volt needs, while maintaining the batteries. The batteries also acts as a capacitor for the high draw items. They work together to provide steady power for the rig. If your convertor is operating as it is designed, you should not overcharge your batteries.

Only speaking regarding the older RoadTreks, If the 12 volt battery/ house battery power switch/ IS turned ON prior to being plugged into shore power the battery charger IS Activated to charge the house battery. If the switch for 12 volt house power is NOT turned on before being plugged into shore power the battery charger is NOT activated.

if the converter is working right it should not over charge the battery.