If it is < 12.60V (but absolutely > 12.50V) the battery must be recharged immediately. If it is < 12.70V, carry out a new check after approx. one month. In the case of recharging outdoors, please ensure that the battery first reaches a temperature above 0°C so that a charge can be absorbed.
If charging is necessary, you can remove the battery and "defrost" it in rooms with >0°C, or simply leave the charger connected to the battery for a few days, at the beginning the charging energy is used to heat the battery. Don't worry, a fully charged lead-acid battery will freeze "only" at approx. minus 70°C. A discharged battery (open-circuit voltage = 12.0V) will freeze at a few sub-zero temperatures!