Update: My replacement Li Time LiFePO4 got its second test last Saturday. I was only perching, so just needed the Terrova for spot lock. However, it was very windy so that required the Minn Kota speed/power to run between 6 and 10. This time, I got about 5 minutes out of spot lock and the Minn Kota shut off. I restarted it and it ran another 5 minutes and died. It did this a few times and then wouldn't turn back on at all. The batteries were fully charged of course.
My theory is that the Minn Kota pulls too high a current when it kicks up to 10 and the Li Time BMS shuts it down. That could be a Minn Kota maintenance problem or it could be that the BMS just won't work with this kind of load.
So I bought two Millertech 100 Ah LiFePO4s. (Thanks for the recommendations). Today was their maiden voyage. It wasn't quite as windy today as Saturday, but pretty close. I did see the Minn Kota spike to 9 a couple times. It never cut out for the 6 hours we were on the water.
Both Millertech and my model of Li Time say they allow a 100 amp discharge, but the Millertech says it will allow 300 amp for 5 seconds. Li Time recently introduced a model with a similar feature. Maybe that's the key for trolling motors - they need that short-term burst.
I must say I love having the blue tooth app which shows me exactly the percent of charge remaining. As a bonus, it also shows me the battery's temperature, which is nice to know because it was a nippy 42 degrees this morning when we started.
We'll see if it keeps working, but my initial impression is good.