Do I need to look for anything special in a charge controller to keep lead-acid batteries from freezing over winter? Gell, AGM, standard deep cycle, etc??
Not really, but your panels could be / should be vertical (not tilted) over winter so snow doesn’t zilch your charging. Keeping the batterieslead acid batteriestopped up will extend their life a great deal
You might want a charger that has temperature compensation for charging voltage. The colder your batteries the higher the charging voltage. Some batteries limit the charging voltage. All depends on the battery manufacturers recommendations.
Ed