why would you switch it only on the charge cycle it makes more sense that you let it swich on temparature of the battery bank housing as this is much more critical for your batterys as your charge voltages are fixted (assumtion)
the battery bank housing should already be ventilated enough for reliesing the produced gasses durring charging in the first place
another aproach could be that you make a charge voltages corection depending on the temparature of the battery
Robert-Jan