Why does the battery in my car drain while driving and the alternator and battery has tested good?
battery May 22nd, 2010We have put a charger on the car and the charge holds while the car is off. But when driving the car the battery drains in less than an hour. The alternator has been tested and shows to be good. The new battery has been tested and shows to be good. The head connectors for the battery have been changed. The problem is still occurring. What could the problem be?
You almost answered your own question. The fact of the matter is the battery is draining because of *lack of voltage. And what provides your battery with a re-charge of voltage? Your alternator.
How did they test it and what did they tell you? It’s pretty obvious it’s not charging between 13.5 - 14.0 volts with the engine running. Essentially the battery is used for starting, playing the radio with the engine off for a short period of time and four way-flasher use in emergencies. The alternator on the otherhand provides amperage to every electrical circuit in the car when the engine is running.
May 23rd, 2010 at 2:31 am
Poor ground between battery and frame / engine
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May 23rd, 2010 at 2:44 am
maybe a big boom box, you might need a bigger alternator..
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May 23rd, 2010 at 2:56 am
Or your alternator belt is not tight enough, or is installed improperly, turning the alternator in the wrong direction.
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May 23rd, 2010 at 3:02 am
has to be either a bad alternator or the battery, you say the battery is newer so I would guess you replace the alternator and see what happens.
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May 23rd, 2010 at 3:37 am
You almost answered your own question. The fact of the matter is the battery is draining because of *lack of voltage. And what provides your battery with a re-charge of voltage? Your alternator.
How did they test it and what did they tell you? It’s pretty obvious it’s not charging between 13.5 - 14.0 volts with the engine running. Essentially the battery is used for starting, playing the radio with the engine off for a short period of time and four way-flasher use in emergencies. The alternator on the otherhand provides amperage to every electrical circuit in the car when the engine is running.
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Alignment, suspension and brake shop.
May 23rd, 2010 at 4:25 am
Alternator & Battery were "Load Tested?" Voltage is good but if you don’t have the "Amps" to push the Voltage then nothing will work properly. "Load Test" the Alternator to make sure you are getting the "Listed" Amperage, Low Amps means Bad Diode(s) that Will Drain the Battery; Battery needs to be "Load Tested" at 50% of CCA (Cold Cranking Amps) for 15 Seconds not dropping below 9 Volts during the Test to see if the Battery will Take & Hold a Charge. Check that All Grounds are Clean & Secure (Battery to Frame & Block, Alternator to Block, Starter to Block & Block Strap to Firewall).
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38 Years Exp.
May 23rd, 2010 at 4:56 am
Ground,there are several;one at neg. post battery; one from neg to the metal that supports
radiator,the Positive, starter post; and the small wire to starter,when you reach for Pos,cable on starter to see if is tight,Make sure you disconnect battery,neg and positive.
If You have the bolt on connections on cables at battery remove them and buy the proper length cable with the ends intact , bolt on clamps will cost You money,and a whole lot of Anxiety;
If the battery is draining in 1 hour You have a major short,this would show a spark when you place the cable on battery;
Do this check at night if not battery then there is fireworks under the hood,you will see it; ;
Electricity flows in a circle out the Postive through whatever need it and the frame rounds up all the strays and sends them home to the battery,It is sort of like herding cattle at roundup;
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Mil,Jet Engine Mechanic, aircraft 27 yrs, auto mechanic since I was a farm boy 60 yrs ago;
Remember D.C. voltage goes out the positive post through whatever needs to work,then to frame and back to Negative post. There is one exception the Alternator,the large red wire has 12 volt d.c. from battery, when car is running the alternator is making A.C. volts,but there is a rectefier that changes volt to 12 volts D.C.
When you read a d.c. volt meter connect to pos and neg ign, is off 12 volts,more or less;now start car 13 volts at the same location;good;