Ceramic heater to heat hydraulics in battery compartment?

I don't think you'd have trouble with a heater in the battery compartment, as long as you are not moving any current thru them or charging them.

The hydro being cold shouldn't be an issue either. I've never seen an excavator or dozer in a heated garage to start and run thru a winter.
Though, getting the tank and pump warmed up sure aint gonna hurt it none.