Voltage fluctuation,nl so start

I have been fighting this for a while. If I happen to stall the car, manual Trans, it will not start again. Something happens that drains the battery, at least that seems to be the correlation. There is sometimes fluctuation in the voltage meter, both on the dash and via obd it will rapidly go between about 13 and 14.8 volts. I had the battery tested last week at 95%, 755 CCA and 12.8 volts after it was jumped. Today it tested at 555 CCA and 90% when I had the alternator tested, after driving 10 miles. The volt meter was steady at the high 13s for most of the drive. Sometimes it holds 14v consistently. I wonder if this sounds like the voltage regulator? I assume that could cause the fluctuation of voltage output. And the reason the alternator tested fine was bc at that point it was working. Intermittently it does not? also today when it died and I jumped it, the psd Nand abs did not work, until I restarted the car, then all was good. tthw battery <1 yr old, I keep it on a tender most of the time. From what I have read it does not sound like the y cable. anything else I should be checking? I have a new regulator and qas thinking about putting that in, but if my problem is Intermittent, it may not be obvious. The battery connections are tight and corrosion free. Thanks for the ideas.

Quotes source post: 20410381

Whats the battery voltage at the battery terminals with a volt meter when it does not want to start..? Does it just crank over slow..? or not at all..? Or does it crank over fast just doesn't want to start..?

It sounds like you have tested the battery for a shorted cell and it has passed. I'd check the ground cable from the alternator to the engine and body next. Then voltage regulator and wiring connections. Intermittent could mean heat (causing a faulty circuit when warm) or vibration (affecting connections) or corrosion (affecting connections) is contributing to generate the symptoms.

Bad stater when it gets hot it gets worse. Its how they fail.

Great ideas, thank you. I looked at the y cable, looked fine, tight. But may replace it anyway. The hot starter would be a surprise as if I let it sit a few days not plugged in it won't start. So I would not expect heat to be the issue. I'll test the voltage w a multimeter. When it does not start, it will weakly crank for one second. The lights in the dash work. But not enough juice to turn it over. Strangely I was at the gas station and it would not start, so i hooked it up to a spare battery, new, and it would not start. A tow truck driver had a jump box that ultimately worked after a couple minutes of being connected. Not sure if that is telling. Thanks for the ideas.

I was watching the voltage right before I shut it off, was basically 14v. But had a no start 2 hours later. I tried to jump it with a new battery, no luck. However when I connected the new battery directly it started right up. Does that imply that there is something with the existing, old battery. Or should that not work? The old battery was ~9volts when I tested with a multimeter. Driving w the new battery, there was still voltage fluctuations when I came off the throttle. Probably not as much as with the old battery. Probably mid 13v to 14v. On the throttle it held at 14v. I tested the new battery voltage at home, was low 12vs. thw battery tray is destroyed!! Looks like the old battery was leaking or some sort of electric corrosion. About 2 years ago i removed the tray stripped it to bare metal and primed and repainted. Now it's covered in corrosion. I wonder if that means something. The battery may have some damage, or it's just dirty. The old battery tested at 95% at AAA and a similar level at Pep Boys. About 580 CCA if I recall. I think I need to replace the voltage regulator in the a lternator and see what happens. Any other ideas? I really think the battery tray is a symptom.

A fully charged and tested battery should be closer to 12.5v than 12v. And 550CCA is not really that high, unless it�s very, very cold outside. You should be getting 750-850 CCA I think. Using a new battery to jump a dead battery often doesn�t work well because a new battery might be 12.5V, and the old battery might be 11.5-12, so that�s only 1 volt difference. Jump starting often works because the other vehicle is running and providing upwards of 14.4V, which actually pushes way more current into the dead battery to assist in the jump start procedure. My hunch is you have bad cables or a bad battery. You cannot often tell just by looking at the cables. Starters do go bad as well. Maybe post a video of your car turning over during starting, and also post one where it doesn�t start. Last thing: voltage fluctuation, if it�s slow, is normal. It will drop below 12 when starting, go up to 14 when charging, then settle down between 12-13 after some time. All normal. If you see the needle rapidly fluctuating, that�s a sign that something is wrong, or if you see voltage at 12 or less after fully charged, something is wrong.

Quotes source post: 20431961

Agree. A battery should have a vent with a vent tube that connects to make sure toxic fumes are vented past the tray towards a safer location. Either the vent tube was not connected properly, or the battery is losing acid or moisture is collecting at the tray and not draining.

It turns out the battery had a small dent in the body. not sure how it happened, it does not really appear to be leaking, or any obvious damage. But putting in a new batter seems to have solved my issue over the last week. My old one was 4-5 yrs old and still tested at 95% capacity by two places. Im sure there is something wrong with it, but seems to be fixed. The voltage stays around 14, occasionally it fluctuates, not sure how stable it should be, but seems to be in good shape so far.

Electrical engineer here. I've posted this a couple times recently. Because I replaced the battery, the alternator and the Y cable all at once, when the car is running it stays a little above 14 when cold and if all the fans turn on at once, the voltage goes just under 14. With your new battery, if your warmed up car with the fans on drops below 13, you have a budding Y cable issue. When that happens, the battery gets less and less of a charge each time you drive it so eventually it has trouble starting. But the problem isn't the battery. The Y cable is badly designed. The wire from the alternator that charges the battery is mechanically bound to a second cable that goes to the battery. That mechanical connection is not weather-proofed so depending on the environment, it starts to corrode. As it corrodes, it creates resistance to the flow of current the battery needs and eventually starves the battery. This is what that two-wire connection looks like after it has gone bad: So, when you see the voltmeter drop below 13 when all the fans turn on, what is happening is that the corrosion acts like a giant resistor. The voltage coming out of the alternator is 14.4V. When the voltage measured on your dash shows 12.4V that means there is a 2V drop through the connection. The alternator can put out 120 AMPS, but let's use 100 because it makes the math easy to do in your head. 100AMPS x 2V = 200 watts. 200 Watts of electricity is enough to heat up and melt the insulation as is shown above.

Interesting. And that would tie out with what I have read otherwise. I'll order one for when it warms up I'll give it a go. Thanks for the advice.

instead of going with the OEM Y cable, I had Battery Cable USA fab me up three OO cables with cable ends and ran one from the jump box to the starter and another cable from the jump box to the alternator, and a third cable to replace the ground cable with 00 also. not a problem drawing amperage thru them cables and all for less than 30 dollars. no reason to run the charge cable back to the starter and then to jump box. Quality Copper Battery Cables Made in the USA! - BatteryCablesUSA

Quotes source post: 20446738

I cant really envision what you are describing, but i am all for improving on OEM. Would you have the dimensions of those cables, or maybe the old order? Thanks

Quotes source post: 20446738

Electrical engineer here. That is Brilliant. I wish I had thought of that. That solution eliminates the corrosion problem with the Y cable. If you want to provide all the data for the cable dimensions for this, let's share it under a new Thread titled: New Y cable that costs $30 and can't ever corrode. For the person who asked how this can work, it simply takes the connection of the two cables on the back of the starter to a connection on the Jump point that is easy to access and keep clean as needed.

Quotes source post: 20470504

This economical mod has been documented in the archives before , but is lost on all but the most seasoned Rennlisters...

Quotes source post: 20470615

Seasoned and daring Rennlisters. Still it is such an obvious improvement. I'm wondering if that cable is the descendant of some air-cooled necessity because of the design of earlier cars or if the bean counters suggested the Y cable because it saves time and money instead of connecting three separate cables and was used in some Toyota?

Quotes source post: 20470671

I think it has more to do with weight savings....Wiring/copper has significant weight to it....Porsche uses the min required for the load... most wires are .035mm or .05mm.....Most other MFG's use larger wire even on very light loads.. I have been in Porsche Factory Training Sessions where they would brag on saving a few grams on an updated part...lol.....They are very serious about saving weight ...And the bean counter will get behind it .. How do you save a few hundred pounds ?? Save a few ounces in a few thousand places !!!!