Winter solar battery charging when you can't add water?

If the solar controller has adjustable setpoints, lower ABSorptionVoltage to lower 14's and duration should be no more than 30 minutes.

lower float to manufacturer recommendations for expected temperatures.

Disconnect all loads on battery.

If batteries self discharge to 'zero' in winter, with all loads disconnected, then they are done for anyway and it does not matter what you do.