Odd issue.. could use input

[Mgicm]

I'm going to add a whole extra layer which I should have mentioned.

I have a dual Battery setup with a battery isolator. The second battery has a inverter connected to it for items we run in thee truck. When checking batteries, the second showed 12.8 volts. The odd thing was when it would not start, I could not get the inverter to turn on at all. Once we jumped it , inverter turned right on. Odd. To further muddy the waters, I have a backup camera on a switch which is plugged into the fuse panel accessory terminal (main battery ). When it would not start, the camera would not work. After we got it running, everything worked well. With 12.5 volts, I would think an accessory item should work well regardless no? Headlights worked fine when it would not start as did horn. Didn't try wipers.

I am going to disconnect the isolator and second battery to concentrate on a single battery.
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