OK let's see if I can stump the collective with this one.

Der Question...
Has anyone used a Conformal Coating to water protect modern cordless power tools?

Background...
I have killed two Milwaukee M18 Fuel tools by light to moderate exposure to water. One was left in the bed of my truck overnight and received a light rain. The other one got wet with a hose while using it to mix grout. Now, Milwaukee's fantastic customer service fixed both... out of warranty... at no charge including shipping both ways and the local dealer even did the pack and ship, and yes, I was completely upfront about what happened to them. They replaced everything inside except the gearbox, switch, circuit board and motor in one, they didn't note what was done to the other one.
A pro class tool shouldn't be killed that easily IMO, but that discussion would be better suited for the "what's your beef page".

All the tools I would attempt to treat are out of warranty.
Link to the "stuff" I was looking at.
http://a.co/5nDidt4

Here is a video of someone treating a Dewalt Drill and testing it by running it submerged in dirty salt water!
https://youtu.be/HSrERT1qv1Q

As a side note I see some Drone owners sometimes treat their drones so they can fly in the rain.

In answer to your question in the other thread: Maybe. That's what some "splash-resistant" mobile devices use. But, in their case, everything is interconnected on a common circuit board. So, when, the board is conformally coated, all the electrical interconnections are protected.