Formula233 wrote:
Update-
Load tested the battery and it failed, but I thought it might be frozen. I put it in the basement and on a charger all night, and the next day it tested good, over 800 CCAs. Put it in and the jeep started fine.
Thought I had it licked but next time there was a below-zero night the battery froze again and I had to warm it up by the stove with the charger on before it would crank. It didn't take much charge (1 amp for two hours) but worked fine, spun the engine over fast once it warmed up. Thats weird to me, I thought the battery should not freeze if it is charged. Battery shows 14.6V with the engine running so it seems like the alternator is working.
Should I get rid of this battery or is there some other problem?
Lead-acid batteries contain a solution of sulfuric acid and water.
The liquid in a fully charged battery keeps it from freezing. HOWEVER, if your battery becomes discharged it can freeze, because most of the sulfate is chemically bound with the lead, leaving a very weak acid concentration in the battery. If a battery is exposed to very cold temperatures below freezing and is not
fully-charged, the sulfuric acid and distilled water inside the battery separate and are not properly-mixed and the distilled water/acid solution can freeze.
As the voltage level drops in a battery, the freezing point (temperature) of the liquid rises....
Voltage does not always tell the true picture of a battery's health, you really need to measure the Specific Gravity of the liquid in a battery which compares the density of the battery electrolyte to that of water.
Specific gravity can be measured using a hydrometer. Most good auto mechanics/shops should have a hydrometer.
As the specific gravity number of the liquid in a battery drops numerically, the freezing point of the liquid in the battery rises.
Low specific gravity of the liquid indicates a low state of charge.
These two charts show the relationships between specific gravity, voltage, and the freezing point of the liquid.
Note: the voltages listed are for a single cell of a typical wet cell 12v battery (~2 volts)
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