Keep Lead Acid Batteries Fully Charged to Avoid the Battery Freezing!

In winter it is important to keep any lead acid batteries stored in the cold – car batteries, truck batteries, pump batteries, solar batteries – fully charged, or they may freeze.  Frozen batteries are battery abuse and not covered under warranty.  A fully charged battery freezes at under -90F.  A completely discharged battery freezes at 0F.  That is, a fully discharged battery is full of regular water, and freezes at the freezing point of water.  The sulphate ions that go into solution in a charged battery are a natural anti-freeze.  Where things get interesting is about 50% state of discharge, where a battery can freeze at -16F.  That is the start of temperatures that are possible in Pennsylvania.

If you use a battery tender to keep a battery charged and the battery is stored where it can get very cold, be sure to have a battery tender that has a cold charging option – the charge voltage is lower at lower temperatures.

DepthOfChargeVersusElectrolyteFreezePoin t-C&DTechnologies-TechnicalBulletin-41-7953

Depth of Discharge vs Electroyte Freeze Point. A fully charge lead acid battery freezes below -92F. A fully discharged lead acid battery freezes at 0F!   A 50% discharged battery can freeze at -16F.  Keep your batteries fully charged in the cold.      Source: C&D Technologies Technical Bulletin 41-7953

A battery freezing has a loose analogy to frostbite in people.  In people once a cell freezes, it can’t be put back the same way and it dies.  That is what frostbite is.  The same is true when a battery freezes.  When the electrolyte freezes, it makes changes inside the battery that can’t be undone.

Letting a battery freeze is battery abuse and not covered under warranty.  Battery specialists identify battery freezing because the case of the battery is swollen from the water ice expanding the battery.  Since vehicle batteries are vented, they only swell when frozen.

Jim Logan
Battery Giant of Pittsburgh
10 St. Francis Way, Suite 9
Cranberry Township, PA 16066

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