freezing battery...what temp.

[jeff m]

At what temps do lead acid cells freeze?

a) a disconnected battery
b) one in a car with normal discharge (clock,alarm,ecu etc)

Mine hasn't just curious

[BB-Q]

Plenty of countries go past -30C with no problems.

[Munter]

Good question. The answer of course is to have a fiberglass mat battery....

[Ledaig]

-68.9 Deg C at full charge

[jeff m]

Ledaig said:

-68.9 Deg C at full charge

Thankyou kind sir

[deeps]

Just to add to that, Wiki said...

"Each cell contains (in the charged state) electrodes of lead metal (Pb) and lead (IV) dioxide (PbO2) in an electrolyte of about 33.5% v/v (6 Molar) sulphuric acid (H2SO4). In the discharged state both electrodes turn into lead(II) sulphate (PbSO4) and the electrolyte loses its dissolved sulphuric acid and becomes primarily water. Due to the freezing-point depression of water, as the battery discharges and the concentration of sulphuric acid decreases, the electrolyte is more likely to freeze."

So what happens if it does freeze? Is it ok to charge, or knackered for good?

[deeps]

Approximate
State-of-Charge
(SoC)
Approximate
Depth-of-Discharge
(DoD)
Approximate Electrolyte Freeze Point

100%
0%
-77°F
(-67°C)

75%
25%
-35°F
(-37°C)

50%
50%
-10°F
(-23°C)

25%
75%
5°F
(-15°C)

0%
(DISCHARGED)
100%
(DISCHARGED)
20°F
(-6.7°C)

So -6.7C for a flat battrey.

[GreenV8S]

deeps said:

So what happens if it does freeze? Is it ok to charge, or knackered for good?

In order to charge, the electrolyte has to be able to mix. If it's frozen solid that can't happen.