New Batteries
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Senior User
Joined: Aug 2011
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From: Virginia Beach
New Batteries
I just replaced both batteries yesterday but the voltage doesnt seem right. On the old batteries my voltage in the morning would be 12.1 or so and drop to 9.5 to 10 volts when cranking so I went and replaced them yesterday but the voltages are close to the same. This morning voltage with new batteries was 12.3 and it dropped to 10.1 when cranking. What gives?
< Samantha...my Co-Pilot
Joined: Dec 2001
Posts: 768
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From: Fallon, Nevada
Battery voltage for fully charged batteries at rest should be around 12.7 to 12.9 volts. Voltage at the batteries after the engine has started and the GPCM times out should be around 14.1 to 14.3 volts with a healthy alternator (cold). When the alternator warms up the voltage should be around 13.6 to 13.8 volts. If you are not seeing these voltages then you will have to look further for a problem. Voltage at the batteries (if everything is healthy) with key on, engine off will be around 11.5 to 12 volts...when cranking they should be around 10.5 to 11 volts or so. Remember that battery output will be reduced with a drop in temperature...those specs I give you are for around 70 degrees F...with cooler temps the voltages will be lower, especially with a high amp draw condition like engine starting. If you have a good sensitive meter you can also look at the "AC ripple voltage" at the batteries when the engine is running...the lower the AC ripple voltage the healtiher your alternator probably is...look for around 0.1 to 0.2 volts or so. If it is much more you you probably have a rectifier problem and charging (current) ability will be reduced. Good luck.
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Senior User
Joined: Aug 2011
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From: Virginia Beach
the voltages are upper 13 to low 14 after alt kicks in and while driving. I just thought that voltages dropping that low after sitting overnight and then cranking meant bad batteries. will that not hurt the ficm with voltages below 12, I have a new ficm i am about to put in but wanted to make sure batteries were good first
Junior User
Joined: Sep 2004
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I just replaced my batteries this past weekend too. I used the Energizers from Sams Club. I put them on at home first thing in the morning and I too noticed the key on/engine off voltage and cranking voltage seemed low compared to the Optimas I replaced. Cranked slightly slower too. The temp that morning was around 45*.
Did you pre-charge before installing them? I didn't.
After 2days of using them they charged and now it's back to normal. Actually cranks faster now than with the previous batteries.
Did you pre-charge before installing them? I didn't.
After 2days of using them they charged and now it's back to normal. Actually cranks faster now than with the previous batteries.
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