I ride in the rain and on muddy terrain. I even have no remorse to immerge my motor a few seconds but I will never intentionally direct the hose on the battery.
It's not a problem to put water on an electrical contact. The issues come when there is stagnant humidity and that could arise if for...
Battery terminals are just this, terminals, simple metallic contacts that don't care about water. With a cable behind that goes to the motor.
I would never leave the battery on the bike and never use direct water, just a humid rag to clean the battery.
The best way to dry the bike is to...
The "OFF" position is here when you remove the wheel or install the chain. Everything is really loose like this so it should be at "ON" for riding.
It definitely looks like a M8000 and not a M8050.
KTM uses the KS LEV DX 100mm so it would be a safe bet. (I have one in 150mm and it works well)
You should measure the max possible length in the tube to see which model can fit.