Plastidip Black Rubber paint.
I bought one of draganfly's fibreglass batterys for my SQ4 and found that it is quite considerately made, but the finish looked hand-brushed, much like a garage door...I suspect either the master is in a bad way or they are needing to put excess release wax on with a paintbrush.
Anyway, I rubbed it down with wet & dry and sprayed it with an Aerosol of Plastidip Matt black rubber paint ( off ebay ).
I now have a battery that looks and feels like rubber and all the unsightly brush marks have gone.
It says in the small print it is acid resistant and reccomends it for use in battery carriers within cars.. So it sounds like just the right stuff for the job.