Hello All,
Thank you for the timely and informative help!
Polarity was NOT reversed.
This battery was one I had purchased new and was one of four I had used as a battery bank for storing solar power when I was dry camping two years ago. Battery bank had been charged. Note: the other three batteries all have 13 plus volts. When I removed the (bad) battery I did notice a very small puddle of "water" in my case. Unfortunately, I assumed it was rain water not battery "water". It may have been the later, thus the 'low voltage".
I did not realize that there was an on-board charger so when I unplugged the charger and into the camper, I was continuing to charge a "suspected" bad battery.
Regarding LED light bulbs: I did contact the manufacturer and they told me
Ashley T
8:00 PM (16 hours ago)
Hello,
For the best results it is better to be between 11.8V and 12.8 volts
I did plug the shore power back in and no more "humming" from the panel so hopefully the worst that will come from all of this is some frazzled nerves.
I am taking a break now, before I try a different (fully charged) battery.
Anything I should watch for or test once I install the "new" battery?
Thanks again,
Caryl