Normal Battery Open Circuit Voltage
06-16-2010, 12:55 PM
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Is it normal for the car battery open circuit voltage (OCV) to be 12.3 volts after being parked and untouched for 48 hrs? The OCV is 12.7V after the car has been driven for about 10 miles, the battery is a new Original Equipment from Manufacturer (OEM) dealer installed and the battery has been registered according to the dealer?s invoice. 12.3V represents a remaining battery charge of only 56% for a wet low maintenance battery according to SI B 61 11 09 and http://jgdarden.com/batteryfaq/index.htm . When I took the car in to service for this issue the service adviser (SA) reported battery is good and no draw detected. The car OCV after being parked and untouched for 2 weeks was still 12.3V.
If 12.3 OCV is not normal what is a standard procedure for a Technician to do for finding the cause. Is an Energy Diagnostic a standard practice for low voltage complaint and does it require much time to run? I don?t believe an Energy Diagnostic was run.. SI B 61 13 05 has a statement ?The vehicle must have had a dead battery before Energy Diagnosis can be performed. Also, fault codes must not be deleted,? which sounds like Energy Diagnostic is only made when customer concern is a dead battery. I?m guessing in my case a concern of a low OCV doesn?t warrant an Energy Diagnostic.
Here?s my calculation of energy used for the car to shutdown and sit untouched for 60 hours
Amps__Duration______ Amp/Hr_______Mode_______________Seq#
_______in Minutes
15.000__3___________0.75__________Reaching Idle state____1
1.500__5____________0.125_________Napping_________ ___ 2
10.000_2____________0.33333333____Consumer Shutdown__3
0.450__50___________0.375_________Almost asleep_______4
0.030__3600_________1.8___________Asleep__________ ___ 5
0.500__2____________1.6___________TCU_____________ __6
____________________4.98333333____Total
Information gathered from SI B61 08 00 and its attachments.
For an OEM battery of 110 A/Hr a 5 A/Hr draw is a drop of about 4.5% of the battery capacity. So the voltage should drop about 0.05V at the end of 60Hrs. At a draw rate of 0.030 A/Hr it would take about 60 days before the battery would drop to 50% capacity. This is assuming a new fully charged battery is in use.
If 12.3 OCV is not normal what is a standard procedure for a Technician to do for finding the cause. Is an Energy Diagnostic a standard practice for low voltage complaint and does it require much time to run? I don?t believe an Energy Diagnostic was run.. SI B 61 13 05 has a statement ?The vehicle must have had a dead battery before Energy Diagnosis can be performed. Also, fault codes must not be deleted,? which sounds like Energy Diagnostic is only made when customer concern is a dead battery. I?m guessing in my case a concern of a low OCV doesn?t warrant an Energy Diagnostic.
Here?s my calculation of energy used for the car to shutdown and sit untouched for 60 hours
Amps__Duration______ Amp/Hr_______Mode_______________Seq#
_______in Minutes
15.000__3___________0.75__________Reaching Idle state____1
1.500__5____________0.125_________Napping_________ ___ 2
10.000_2____________0.33333333____Consumer Shutdown__3
0.450__50___________0.375_________Almost asleep_______4
0.030__3600_________1.8___________Asleep__________ ___ 5
0.500__2____________1.6___________TCU_____________ __6
____________________4.98333333____Total
Information gathered from SI B61 08 00 and its attachments.
For an OEM battery of 110 A/Hr a 5 A/Hr draw is a drop of about 4.5% of the battery capacity. So the voltage should drop about 0.05V at the end of 60Hrs. At a draw rate of 0.030 A/Hr it would take about 60 days before the battery would drop to 50% capacity. This is assuming a new fully charged battery is in use.
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