What is the difference in usage between crenulate and crenelate?

I've long been familiar with crenulated edges, but until today I wasn't aware of crenelated. Looking at the definitions, they seem to describe the same kind of feature, that of notches on an edge that are more rounded in contrast to, say, serrated.

What are the differences in nuances? When would be a "wrong" time to use one over the other?

Crenulate is apparently the diminutive of crenelate, so you should use crenulated for small things and crenelated for large things. The distinction between large and small is somewhat relative, but for instance leaves are crenulated, battlements are crenelated.

I have generally heard "crenulated" for living things and "crenelated" for inanimate things, but that may be because architectural features are large, and leaf and wing margins are small.

Crenulate is the diminutive of crenate (having rounded, scalloped teeth), and does not refer to the size of the object but rather to the size of the "teeth": if they're small and fine, use crenulate. Both terms are commonly applied to things in the natural world.

Crenelated is an architectural term meaning "furnished with crenelations", as in the battlements on medieval castles. The crenelations were usually regularly spaced rectangular projections. I suppose you could use the word to describe rounded or irregular projections, but it would be very misleading.