2019 MW Test Panel light is Dim?

[Kacordy]

Last night I stepped into the MW to verify all my water levels, battery levels etc. I held down the test button and the panel lights barely came on. I was very shocked and concerned when I saw this. I went ahead and pulled the black cord to plug it in and realized 6 weeks ago, the last trip, I had failed to plug the black cord into the electrical box inside the cord storage unit. I plugged the cord in overnight and just checked everything 24 hours later. I unplugged the cord and now the test panel lights are bright as usual. I just plugged the cord back in for another 24 hours of charging and the panel is correctly lit up. Why was the panel Dim. Did I leave something on in the MW and the batteries were dead? I hope I did not run the batteries flat and damaged them? This is my first RV. I really appreciate everyone thoughts and advice. Thanks, Allen