Shore power on, idiot lights should show Full (from converter voltage). Turn off all DC loads and disconnect shore power. Idiot light might drop to Green "Good" or soon will after turning on a light or two.
Turn on some lights and fans. Idiot light should drop one light from Green to Yellow "Fair". If it drops to Red last light, that is not a good sign.
Turn off those lights and fans. Idiot light should go back to Green "Good" from Yellow "Fair".
If you leave the lights and fans on for a long time the light will stay at Yellow "Fair"---that would be normal from the battery being run down about half way. Recharge it.
If it is Yellow Fair and drops to Red under lights and fans load, you went down too far (battery less than half full) but it should bounce back to Yellow no loads. If it stays Red and does not go back to Yellow, it is really low.