[mlzook]

Went out to start the car this morning (93 Sierra), and it turned over very slowly and then did nothing. I just assumed it was a flat battery (sounded like one) but at about 12 o'clock the Mrs. went out to start it and it started first go. Could the water in the battery have frozen and caused this caper? It's got me buggered! Any help is appreciated

~Mark

[royce]

batteries state of charge does change with temperature

[mlzook]

That much? Probably near empty too. Should check that!

[Reubs]

My 2c. Only read bold points if in a hurry...

A batteries output is decreased at cold temperatures.

Your car battery is rated in CCA - Cold Cranking Amps. This is how much current the charged battery will produce if shorted at -18 degrees c. The same battery rated in MCA - Marine Cranking Amps (measured at 0 degrees c) will be a significantly higher figure. E.g. 300CCA might be 420MCA for a particular battery. At room temperature the battery will produce a higher output again.

The same applies for the Amp Hour (A/hr) rate. E.g. at 40 degrees c, you may be able to charge the battery to 102% of its capacity it would hold at 24 degrees. Equally, at 10 degrees, the battery may only hold 90% capacity. Note that although the same battery may hold more charge at 40 deg, if maintained at this temperature it's lifespan may be cut in half.

If your battery is almost drained but not dead flat on a very cold morning - try pouring boiling water over it and waiting for it to warm a bit - usually you can crank the engine a few more times and it may start.