I can't think of any reason to keep them from freezing, as long as they're
protected from moisture.
The biggest problem with bringing them in from the cold is that you're
inviting condensation on the tools, including inside parts that are exposed
through cooling vents, etc. That could kill them in short order.
My shed roof leaks, but I'm not stupid enough to use an angle grinder that
was dripping wet - and I would (and did) move the grinder to a part of the
shed that didn't get dripped on.
For the OP's information; a grinder that froze after getting soaked under a
leaky roof might be frozen solid and on application of power the heat from
the windings may burn them out before melting the ice that stopped the
That should give some perspective on the amount of abuse power tools can and
The straight mains hand drill that I keep for clamping in the vice to spin a
wire brush or grinding arbour, was a freebie - the brushes holders had
corroded and jammed the brushes off the commutator, it was a dead simple
repair, just whip the brushes out, clean the holders and re-fit the brushes.
The sort of fault that wouldn't surprise if they happened to any of the
power tools I leave out in the cold damp shed - but none have yet.