I had the 320 Watt battery. It was on sale for $430 at the time here -
https://search.defender.com/?expression=1416-00&x=0&y=0 - Now it shows $490.
I never saw the battery submerged in any water. It was when I returned to the Kayak and I got an 06 error. As I was diagnosing that I disconnected the battery, picked it up and heard some water inside it. Everything was dry on the outside of the kayak at this time. Since I wasn't out in the water for a few days the only thing I could imagine was the rain and we did have a heavy one the night before.
Torqueedo thinks that the scupper holes didn't drain the water fast enough so it would have been sitting in an inch of water.
From Torqueedo:
"The battery is IP67 meaning it can exposed up to 3ft of water for 30 minutes. After 30 minutes the fiber membrane will get saturated and allow water to enter the battery. The battery sitting in 1” of water for 30 minutes will get water inside just like a battery in 3ft of water."
There is a hole on the bottom of the battery so maybe that is where the fiber membrane failed. Previously I never knew a hole was there or understood that it was so fragile to extended water (like rain). I could have easily setup a better system to keep it safe but I figured I was using everything as intended with my initial setup.