Weird issue - battery or alternator?

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jp28173

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2 days ago I was sitting in a parking lot on a phone call, engine off but acc was on and fan was blowing, radio on, phone charger plugged in, for prob 25 mins or so. Went to crank it up and it wouldn’t start. Blamed it on myself for losing track of time with the important call I was on, got jumped, drove home with headlights on just fine. Dash read 13v most of the way, sometimes would be 14v. Drove home 15 mins, parked it and turned off, then cranked it 2 times to see if all was still good and it was fine. To be safe, I put my battery tender on it overnight and by morning the light was green.

Yesterday I hopped in to go take care of some things around 5pm. It cranked up fine, ran fine, and I drove probably 50 miles and engine had been running for almost 2 hours straight at this point. I got to a gas station and shut it off, cranked it up 5 mins later and was perfectly normal. Got home around 8, parked it for the night. Again everything yesterday was 100% normal both starting and running. Dash was consistent at 13-14v.

Today, went to start it around the same time (5pm) and the battery sounded noticeably weak, but it started the engine. I pulled out the driveway and went to accelerate and it wouldn’t go up past 1800 rpms and was extremely erratic with the gas pedal responsiveness. I pulled over and let it idle for awhile thinking maybe the battery was in fact bad after all and just needed to charge back up to get me running normal again so I could go get a new battery, but after 20 mins of running the engine it still acted the same. Even in park or neutral if I floored it it wouldn’t go above 1800 rpm’s and was still very erratic, felt and drove the same way it would if I was running out of gas (definitely am not) and hoping to make it home. The dash said 13v the entire time during all of this, and even 14v occasionally, but also dipped to 12v a time or two when I turned the ac and lights on to “test” it. Got home and turned it off, then tried to crank it back up (thinking maybe it was in some weird limp mode and needed to be reset) but it wouldn’t crank. Voltage on dash was 10-11v.

Anyway, no dash lights have come on throughout this entire process at any time. Does this sound like a bad battery that won’t accept a charge or a bad alternator? And how would you recommend determining which one it is considering I can’t take it in anywhere (unless I fully charge the battery and hope for the best)? Also I don’t fully trust those auto part store testers, they are far from accurate.

Any input is welcome. The battery is one thing but the super rough running when accelerating has me concerned more now. My old Tahoe would throw a code on the dash when it was in limp mode, but as mentioned zero dash lights at all in this process.

Also battery is “ultra start” which I’ve never heard of and has a sticker with Jan 2020 punched out, and another sticker that says 18 mos (warranty period I’m sure). So it’s definitely overdue for changing but how common is a bad battery to not accept a charge from a good alternator and also cause running/peformance issues ? Where would you start if this was your truck dead in the driveway with the hood up?
 

RamDiver

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After 4.5 years in service and your description, I'm with StateOfMind, it's time for a new battery.

Due to my working in a technical field during my career, I would use a toaster-style battery load tester to prove the battery is bad. Mainly, because I refuse to not perform basic troubleshooting and analysis, even when I can forecast the test results.

And I know exactly where I have my load tester stashed. :cool:

.
 

62Blazer

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Yes, very common for a bad battery to not accept a charge. I've seen vehicles where the batteries were so bad you couldn't even jump start them. Actually had to disconnect the bad battery first and hook the jumpers direct to the battery cables.
A quick check is to get a basic voltmeter (commonly found for $20-$30 at any hardware or auto store). Check the voltage on the battery with the engine off. Then start the engine and see what the voltage is at the cables.
A charged battery typically shows 12.4-12.8 volts. Get below 12 volts and good chance it won't start, and obviously 10 volts is pretty much completely drained. Once you start the engine the alternator should be putting out at least 13+ volts and up to mid 14 volts. If you see the 13-14 volt range with the engine running that typically means the alternator is good.
 

RamDiver

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Yes, very common for a bad battery to not accept a charge. I've seen vehicles where the batteries were so bad you couldn't even jump start them. Actually had to disconnect the bad battery first and hook the jumpers direct to the battery cables.
A quick check is to get a basic voltmeter (commonly found for $20-$30 at any hardware or auto store). Check the voltage on the battery with the engine off. Then start the engine and see what the voltage is at the cables.
A charged battery typically shows 12.4-12.8 volts. Get below 12 volts and good chance it won't start, and obviously 10 volts is pretty much completely drained. Once you start the engine the alternator should be putting out at least 13+ volts and up to mid 14 volts. If you see the 13-14 volt range with the engine running that typically means the alternator is good.

As much as I agree with everything above, I would add 1 caveat for the less familiar.

A battery that is measuring at a reasonable float voltage, 12.6 - 12.8, could still be hiding a flakey cell that only misbehaves under a significant load like that of a starter motor.

This is where the $20 toaster-style battery load tester from HarbourFreight is the definitive device for proof of performance testing on batteries.

I think everyone should own a multimeter especially those who own a vehicle that they perform any basic maintenance upon. HarboutFreight or Walmart have many inexpensive options.

.
 
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DRam2019

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Had a similar experience with my 2500. Would hit start button and every so often I’d hit button and get one click, would try again and it’d be fine. Would go several days without an issue, then would do again. Replaced the battery and 2 days later, click. Checked battery terminals, all good there, ended up being loose main battery cable on starter. Tightened up and no problems since.
 

62Blazer

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As much as I agree with everything above, I would add 1 caveat for the less familiar.

A battery that is measuring at a reasonable float voltage, 12.6 - 12.8, could still be hiding a flakey cell that only misbehaves under a significant load like that of a starter motor.

This is where the $20 toaster-style battery load tester from HarbourFreight is the definitive device for proof of performance testing on batteries.

I think everyone should own a multimeter especially those who own a vehicle that they perform any basic maintenance upon. HarboutFreight or Walmart have many inexpensive options.

.
Yes, the above is correct. There are cases where the battery can say 12+ volts but can't provide any amperage.
 
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Tominator223

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Put a meter on bat. While running . That’ll tell if alt is good. Check cable ends. Bad crimp can be a issue. Or loose connection . And load test bat . With toaster style tester as mentioned above. It’s usually something simple that give the most issue. Like getting one lil paper cut.
 

Wild one

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An old school method to check the alternator in the field if you didn't have a multimeter handy,was to use a screwdriver and touch it to the back bearing,if the alternator is charging,there'll be a pretty decent magnetic field that should grab the screwdriver and suck it towards the back bearing,if no magnetic field,good chance the alternator needs replacing
 

stormcom

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You need a battery. Only get an AGM and the best one you can get. They are beasts on batteries. I use Interstate AGM HD and have had very good luck. You definately need a battery.
 

mikeru

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An old school method to check the alternator in the field if you didn't have a multimeter handy,was to use a screwdriver and touch it to the back bearing,if the alternator is charging,there'll be a pretty decent magnetic field that should grab the screwdriver and suck it towards the back bearing,if no magnetic field,good chance the alternator needs replacing
I've used that method many times over the years. Only I was taught to do that test on the front of the alternator because it's not always easy to get to the shaft on the back side. And it's possible to short out the positive terminal on the back of the alternator if you're not careful. Although you also have to be careful if using the front because of the spinning belt LOL.
 

turkeybird56

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I've used that method many times over the years. Only I was taught to do that test on the front of the alternator because it's not always easy to get to the shaft on the back side. And it's possible to short out the positive terminal on the back of the alternator if you're not careful. Although you also have to be careful if using the front because of the spinning belt LOL.
Quick way in front take off a finger, LOL. Only caveat no mechanical fan, hopefully, hopefully e fan, or OP betta watch for that fan, quick way to chop off hand or finger.
 

turkeybird56

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Yes, the above is correct. There are cases where the battery can save 12+ volts but can't provide an amperage.
YUP, had an AGM when running read 14.2 +++ charging, but when off, and put on meter, showed 0% in SOC.
 

Hardracer

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Has the OP ever come back?
 
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