Car battery idling, charging and its life

My car battery will be seven years old this October 2015; I needed to use a battery booster to jump start it myself while I was at a Redbox kiosk location after picking up the DVD movie “The Water Diviner” (2015).  The battery could start normally in the past few days, but I think I need to replace it in a week myself.

During my process of evaluating a suitable car battery (group size 47 for the climate in southern California), I find this following quoted article “How often do I need to use my car to prevent battery death? ” by Jason Tchir brief and informative.  The article is on this web page


“People have to realize that the vehicle’s alternator or generator is made to maintain the battery and not charge it back up once it is low,” Feist explains. “So, if the vehicle is left for long periods, this can put unneeded stress on that system.”

If you’re not going to be driving that often, just idling the car will do your battery more harm than good, Brown-Harrison says.

Starting the engine draws 100 to 130 amps, and idling the car for 15 minutes might put back three or four amps,” Brown-Harrison says. “If you’re idling only for 15 to 20 minutes, the battery never truly gets recharged. So each time you start and leave it to idle, the charge will get lower and lower and lower.

Even if you’re driving every day, but only for short trips to the store, you’re shortening the life of your battery because it never fully recharges.

Realistically, you have to be in excess of 1,000 rpm before it starts charging,” Brown-Harrison says.We used to say that a battery would last five to seven years, but now that’s dropping to three to five years. That’s because fewer people are making those long commutes that give the system a better chance to do its job properly.

And yes, when I bought my current car battery in 2008, its warranty was 84 months; now most car batteries only carry 3-year or shorter warranty.

Additional information from this article “Diagnosing A Car Battery That Runs Down” on

A fully charged battery should read over 12.6 volts. If the battery reads 12.45 volts or less, it is low (less than 75 percent charged) and needs to be recharged.

Battery Voltage and State of Charge:

12.66v . . . . . . . . . . 100%
12.45v . . . . . . . . . . 75%
12.24v . . . . . . . . . . 50%
12.06v . . . . . . . . . . 25%
11.89v . . . . . . . . . . 0%

(NOTE: these readings are at 80 degrees F. Battery voltage readings will drop with temperature roughly 0.01 volts for every 10 degrees F.)
(At 30 degrees F. a fully charged battery will measure about 12.588 volts, and at zero degrees F it will measure about 12.516 volts.)

After charging the battery or jump starting the car, connect the voltmeter to the battery the same as before and not the charging voltage. A charging system that is operating normally should produce about 13.8 to 14.3 or more volts at idle. If the charging voltage is less than 13.0 volts, the alternator is not putting out enough voltage and current to keep the battery charged. You should have the alternator tested (or bench tested at an auto parts store). If the current output is not up to specifications, replace the alternator.



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