Lead-acid batteries will self-discharge when not in use.  The rate of self-discharge increases as ambient temperature rises.  As a precaution, stored batteries should be recharged every 3 months until put into service to avoid over-discharge, sulfation and possible freezing in cold temperatures.

Winter Storage


Prior to placing batteries into winter storage make certain the electrolyte level is 1/4" - 1/2" (6-13mm) below the vent tube. The electrolyte level in very cold batteries will lower slightly.  It is best to allow the batteries to warm to a normal ambient temperature before judging electrolyte levels.

Once the electrolyte level is correct to ensure that the batteries are fully charged. Ensure that the battery tops are clean and dry.


Now the choice is whether to leave the batteries connected to your charging system or remove and store in a cool dry area. In marine applications, if the batteries are stored aboard a boat, charge completely and disconnect the terminal cables. This will prevent premature discharge of the batteries due to a ground in the electrical circuits or failure to turn a piece of electrical equipment off.

If a battery becomes discharged to 50% SOC, the electrolyte may freeze when temperatures drop to -15° C (5° F) or below. 

Temperatures at which electrolyte, in various states of charge, starts to freeze.

Specific Gravity

(cor. to 80° F/26° C)
Freezing Temp
1.280 -92° F (-69° C)
1.265 -72.3° F (-57.4° C)
1.250 -62° F (-52.2° C)
1.200 -16° F (-26.7° C)
1.150 +5° F (-15° C)
1.100 +19° F (-7.2° C