The problem is not, that you need to turn off the charger
The problem is you did not give the batteries time to recover
And the charger did what it was supposed to do
But yes with some magnum models you can set the power input level to a lower level, and minimize the charge power used ( tell it you have a 10 amp power source )
Post the model number of the magnum
Somebody will be able to give you the instructions for changing the power settings
P.s.
I would have used the generator for the MW, so the batteries stayed charged and then there would not be any surge drain / charge on them and I could turn on the the A/C
Btw
We have 600+ watts of solar and 675 ah of AGM batteries, and a 3000 watt generator,
And I prefer to use the generator for the MW, unless it is quiet hours
During the day we use the generator
And if I need to switch on the A/C , possible over load conditions are minimized, because there will not be a big charge surge replacing what I just took out
