It was over heating up (code 41) with the old batteries too.
Ah, It seems we may be narrowing it down then.
I seem to remember another related thread that mentioned that too many -41 errors will eventually kill a controller. - Just something to think about.
Depending on where you are right now in your project you might want to do something about this quite soon.
- see what you can find for thermal paste and spread some between your controller and frame plate.
- since you are next level hotrod you might upgrade to some sort of heat sink under there. Maybe even install a fan.
For inspiration I submit a link to a thread that started back in '17. Reading through it, the concept seems to have had some legs and a possible solution to your problem.