Help with Battery voltage
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Joined: Oct 2006
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From: San Antonio Texas
Help with Battery voltage
Hey guys I have been having problems with battery. What should be the normal operating voltage? Mine is about 13 to 13.3. Shouldnt it be in the 14.5 range?
Thanks
Thanks
Safety Car
Joined: Feb 2007
Posts: 4,939
Likes: 448
From: CHOCOWINITY NC
A fresh battery will have a resting voltage of around 12.7V. (measured at 65 degrees after sitting with no draw for 12 hours). The only way to measure this accurrately is with a digital voltmeter AT the battery terminals. Just switching on your car will skew the numbers as you're throwing a bunch of power draws into the equation which will lower the V. readout. When an alternator is running it will put out between 13.5 and 14.1 volts into the battery depending on the batteries state of charge. This voltage is regulated by (duh!) a regulator. A batteries ability to hold and accept this charge has nothing really to do with how much you're trying to stuff into it. A fully charged battery will generally show an alternator supplied voltage of about 13.7 V depending on the voltage draw of the cars electrical systems.The Corvette seems to have a relatively high charge rate which I believe is partially responsible for the early demise of batteries in this car. A battery with a low charge will typicallly show 14V-14.4V or so as the battery capacity is replenished by the alternator output. A totally bad battery may not accept a charge at all. A higher charge rate will show at the first start of the day as the battery recovers lost voltage from sitting and parasitic draws as well as needing to recover from a high load engine start. Batteries naturally age and over a period of time their ability to hold a charge and full voltage diminishes. At 4 years or so this usually drops to about 50% of the original capacity. A bad or shorted cell can also cause failure as all cells need to be fairly consistant...
Test a battery by either:
1)Taking a resting voltage reading
2)doing a load test
Test an alternator by:
1)measuring voltage while running. Anything over the batteries resting voltage means it's putting out. Voltages less than 13 or so means it's not putting out enough..Sometimes a bad or shorted battery will not accept any voltage even when the alternator is good.
Test a battery by either:
1)Taking a resting voltage reading
2)doing a load test
Test an alternator by:
1)measuring voltage while running. Anything over the batteries resting voltage means it's putting out. Voltages less than 13 or so means it's not putting out enough..Sometimes a bad or shorted battery will not accept any voltage even when the alternator is good.
Last edited by Modshack; Aug 25, 2008 at 10:26 PM.
Thread Starter
Pro
Joined: Oct 2006
Posts: 747
Likes: 0
From: San Antonio Texas
A fresh battery will have a resting voltage of around 12.7V. (measured at 65 degrees after sitting with no draw for 12 hours). The only way to measure this accurrately is with a digital voltmeter AT the battery terminals. Just switching on your car will skew the numbers as you're throwing a bunch of power draws into the equation which will lower the V. readout. When an alternator is running it will put out between 13.5 and 14.1 volts into the battery depending on the batteries state of charge. This voltage is regulated by (duh!) a regulator. A batteries ability to hold and accept this charge has nothing really to do with how much you're trying to stuff into it. A fully charged battery will generally show an alternator supplied voltage of about 13.7 V depending on the voltage draw of the cars electrical systems.The Corvette seems to have a relatively high charge rate which I believe is partially responsible for the early demise of batteries in this car. A battery with a low charge will typicallly show 14V-14.4V or so as the battery capacity is replenished by the alternator output. A totally bad battery may not accept a charge at all. A higher charge rate will show at the first start of the day as the battery recovers lost voltage from sitting and parasitic draws as well as needing to recover from a high load engine start. Batteries naturally age and over a period of time their ability to hold a charge and full voltage diminishes. At 4 years or so this usually drops to about 50% of the original capacity. A bad or shorted cell can also cause failure as all cells need to be fairly consistant...
Test a battery by either:
1)Taking a resting voltage reading
2)doing a load test
Test an alternator by:
1)measuring voltage while running. Anything over the batteries resting voltage means it's putting out. Voltages less than 13 or so means it's not putting out enough..Sometimes a bad or shorted battery will not accept any voltage even when the alternator is good.
Test a battery by either:
1)Taking a resting voltage reading
2)doing a load test
Test an alternator by:
1)measuring voltage while running. Anything over the batteries resting voltage means it's putting out. Voltages less than 13 or so means it's not putting out enough..Sometimes a bad or shorted battery will not accept any voltage even when the alternator is good.
Dang, thanks for the feed back.
Safety Car
Joined: Jun 2004
Posts: 3,563
Likes: 2
From: Dallas Tx
If you have a DVOM. After the car has been sitting a few hrs, open the hood and check battery voltage right at the battery with everything off. It should be around 12.5 to 12.7, somewhere real close to that. Each cell should be about 2.1 volts, and you've got 6 of them.
Give it a good drain for about 15 minutes, leave the doors open, run the radio... Then start it with the DIC on voltage. Right after start up it should show a pretty high reading - above 14. Most mine have said 14.5 right after start up and then after a little driving start coming down into the 13 range. If yours is never getting above 13.3, even at start up, may be worth having it looked at.
