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Old 12-23-2010, 03:27 PM   #1
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Join Date: Apr 2009
Location: Boston
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My Ride: '01 325xiT, '85 M635
Minimum voltage to start car?

Hey All. Left my lights on the other day and killed my battery. It is now on my charger being charged but I want to get on the road. I am wondering, what is the minimum volatage for a stock battery that will start the car? Any ideas?

I am wondering if I can pull it off the charger at 12.3 V or so and still start the car? Dont want to bring it out and install it and then find out It isnt charged enough.

I did see this, but not sure how low I can go.

Open Circuit Voltage (12 V) Approximate charge
12.65 V 100%
12.45 V 75%
12.24 V 50%
12.06 V 25%
11.89 V 0%
...................2001 325Xi Touring..................1985 M635Csi..................
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Old 12-23-2010, 06:53 PM   #2
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Location: North Brunswick, NJ
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You cannot tell by voltage alone if a battery will start a car. The battery needs to deliver a few hundred amps to crank the engine, that is the more important factor. Condition/age of the battery has a lot to do with it. If you are not sure, wait a little longer. When the car is acually cranking battery voltage will commonly dip as low as 8-9 volts in a properly working system.

Last edited by kbsilver; 12-23-2010 at 06:54 PM.
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Old 12-23-2010, 09:37 PM   #3
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+1^. Voltage with no load tells you very little.
'04 330i ZHP - OEM Clears - ///M Strut bar - CoolantSnitch
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Old 12-23-2010, 10:28 PM   #4
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I guess I don't understand the question.

Put the jumper cables on, or put the charger on, and start the car and hit the highway. The battery will charge in a half hour under most conditions. If you are planning on a drive of a couple of hours, then the battery should fully charge by the time you get there.

How do you leave the lights on? My car screams at me with an annoying buzzer that tells me the lights are on and the door is open and the key is off. Pretty hard to miss it.
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Old 12-23-2010, 11:48 PM   #5
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My Ride: '01 325xiT, '85 M635
i live in the city so no outlet near car. Had to pull batt and throw on my charger in apartment. I got it to 66 percent, about 12.5 V and started no problem.

i am really suprised i miss the buzz. I had a bunch or stuff to unload and live near the airport. Maybe there was jet noise right when I got out. really wierd.

i understand the whole amp thing quite well but on a good battery, all you have is a volt meter to know if it will work or not.
...................2001 325Xi Touring..................1985 M635Csi..................
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