Battery Voltage vs. Temperature

Checked mine after the car sat for 18-20 hours in the garage. It's about 60 degrees F at the moment. Read 12.28 volts according to my digital voltmeter. That means I lost 1/3 of a full charge from maybe a 30-degree drop in temperature and sitting? It read 12.54 the last time I checked. I did not have the alarm set either time. The battery is about 2 years old. I'll need to check it under the same conditions when it gets warmer again, perhaps I didn't wait as long the last time. Charged my jump box fully, just in case.

Of note is I checked the battery voltage with my VCDS using the engine module's advanced measuring vales, and the label, battery voltage. It read only 12.0 volts. My digital voltmeter is a decent autoranging Sperry that's supposed to self calibrate.

Fed, redo your math. If you're at 12.28 volts now, to have lost 1/3 of your full charge would mean that your starting point would be nearly 18.5 volts.

Al_in_Philly said:

Fed, redo your math. If you're at 12.28 volts now, to have lost 1/3 of your full charge would mean that your starting point would be nearly 18.5 volts.

Click to expand...

I can't find the chart I used but this chart shows about a 50% loss for AGM. One volt is the difference between 100% and 0% charge for LA car batteries

https://www.energymatters.com.au/components/battery-voltage-discharge/

Temperature vs. amperage, voltage, and capacity is a very complex topic, having to do with the availability of electron sites. I suspect that the temperature difference completely obscures our ability to draw a conclusion about drain. According to a battery test chart from Carquest, you could expect about .3-.4 volt drop from the temperature. (http://www.carquestprofessionals.com/batteries/maintenance.html)

I guess just wait until it's a constant temperature out to test the drain...

Shawn

Automotive batteries consist of six 2.1 volt cells. 12.6 volts is the maximum charge. Anything above 12.2 is normal.