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well winter is almost here and we all know that means battery voltage will drop a bit. if you have an older battery that does not hold full charge, the drop could be enough to cause problems starting the car. if you check your voltage with a multimeter at 30F and it reads 12.5v you should be okay. if it read much lower, try to recharge the battery first with a slow 1-2 amp trickle charger, then replace it if that doesnt work.

Battery voltage and charge state:

12.68v = 100%
12.45v = 75%
12.24v = 50%
12.06v = 25%
11.89v = 0%

Dont forget these values are at 80F. At 30F they will be a bit lower. For example at 30F a fully charged battery will read 12.58v

A reading of 12.4v or less indicates a low or discharged battery. If after charging the voltage is still low, replace the battery.

 
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My advice, buy a gauge for the 12v socket. It'll tell you if your alternator output is good, and display your battery voltage.

I just keep mine plugged in.

 
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@ Gearbox: Got battery voltage tested at Autozone a few hours back. It read 12.55V @ 55F. The meter they had said bad battery. I still have the stock battery on and I know it will go but according to the values you posted do you think it need to replaced right now?
Yesterday it was in the lower 40s and it skipped the first time I tried to start it in the morning but started in the second attempt.

 
Rep Power: 813

yeah guess i shouldve been more specific. these general voltage readings only apply if you have confidence in your battery (if its relatively new like under 2 yrs old). if you load test a battery with the auto store machines and it fails, theres a good chance its bad. voltage is only part of the battery equation. amps are really the most important thing and you need a load tester to measure that. i would go ahead and replace it before the thing dies for good. the easiest way to tell is listen to the starter. if it sounds sluggish and low toned when turning, the battery is struggling to provide the necessary power. while hot weather is more damaging to a battery than cold, a battery will lose capacity naturally in colder climates. this does not mean cold is killing the battery but rather the battery is not able to produce the same level of power than in the summer. battery warmers can help a ton in the winter. in the summer you want a battery cooler to extend life.

if its been 4 yrs, i would def get a new battery. $100 every 4 yrs is nothing and well worth the trouble you will avoid if you wait til the battery dies. having a newer/working battery also helps the car run better because the alternator and other systems are not stressed trying to squeeze out more juice to keep charging a failing battery.

 
Rep Power: 353

battery tender plus FTW

 
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@ Gearbox: I will play it safe than sorry and replace the battery...thank you.