Bad Alternator, Really?!

So went to start my truck today, and my battery was dead. Very strange seeing how I just replaced the original about 2 months ago. Tested it at Oreillys. Bad alternator. Said sometimes a bad battery cell can throw the test, so I pulled the battery out charged it and tested it again. Good battery. My 2015 has 29,000 miles. I find it very hard to believe my alternator crapped out. I have some aux lighting, but they're all LED. I did install seaters a few weeks ago, not sure if that could have done anything? My positive terminal was also very corroded so I cleaned that up. Put everything back in and it fired up. Going to see how this week goes. Any ideas fellas??

 

Did you get a voltmeter and check voltage with truck off vs idling to see if the alternator is charging okay? Should be a voltage difference of about roughly 1.5 volts

 

When you pulled the battery and tested it. Was it right after charging? Surface charge can make a bad battery look good. I have a cheap load tester that works pretty good to tell me if a battery is in need of replacement. I use it more for my boat batteries.

 

I have a multimeter, but still need to play with it a little as Im not the most electronically inclined. I don't know how to read them

No crossings or washings whatsoever. This isn't my DD so it sometimes sits(about 10 days since last drive) which is another potential cause right?

yes it was pretty close. I pulled it, they said it needed an hour to charge before they could test. They called me an hour later and said the test came back as a good battery

 

https://www.youtube.com/watch?v=Bzz7P3qNHcE

 

Using @Hit n Run 's video here are my results:

Off- 12.33
On-13.94
On with load- 13.85
Off again- 12.51

 

It was 4 "clicks" in quick succession, then silence( when my original battery died it was complete silence). My initial thought was I left something on, but couldn't find anything. My second thought was the new seat heaters, but they were in the off position, and plus they have a relay. Maybe ill take them off the battery for a few weeks and try that?
Can you clarify on "load test"? I did 3 tests, the original handheld test in the oreilly parking lot, the 2nd test when I left them the battery to be charged on the shop unit, and my personal multimeter test. Here are the results from the oreillys shop test

 

Appreciate the help brother. I'm going to keep a very close eye on it all week. Thanks again!

 

You could check the battery after it sits to see if it stays over 12V.

 

FYI- I removed the right 12v power port and made the opening rectangular to hold a digital panel mount voltmeter. It was an EBAY special under $10.00 IIRC. I just clipped off the power port wires and attached them to the voltmeter. I never wonder about alternator output and I don't miss the outlet. I added a two port 20a hot always outlet and it's more useful. I later found a round voltmeter is available and it should fit into the area easier if not exactly.

 

That off reading of 12.33 is a little low, may be a weak battery. Try turning the headlights on with the engine off and see how quickly the battery drains down. A strong battery should still be in the 12.0 range even after the lights are on for a couple mins. If it drops down near 10.0 its weak

 

A fully charged battery is 12.7. Test it and then turn on your head lights if it drops to 11.7 in short order it's toe up. Alternators are voltage dependent that is how they are regulated 13.8-14.2 is pretty normal.

 

Question:

If i disconnect the positive cable from the battery when truck engine is running and the engine dies. Would that tell me the alternator is bad?

 

DON'T DO THAT!!!!!!!!

That's a good way to fry a bunch of electronics.

 

Thats not good for the electrical system on the truck. Should be avoided..

 

The battery crapped out in my 2015 the other week - same scenario, I have ~23k miles. My wife's crapped out in her 2015 highlander in the first 14 months. On occasion when I would go out into the garage I would hear a hum, these cars have something running for emissions every so many hours so if you don't drive you vehicle regularly it will eventually drain the battery. I replaced both with the X2 power which is a rebranded Northstar. I also purchased a battery tester which tests voltage, voltage under load, and alternator output to make sure it was the battery and not the alternator. Good luck.

 

Thanks for the responses. It was just a question. Had someone tell me to do that years ago.

 

OP, I truly believe that your issue was from corroded terminals which will cause no starts or low battery like issues. If you really did cleaned and tightened the terminals, you should be fine now. This would explain why your battery tested good and your voltmeter load tests showed a good alternator output.

 

It was the corrosion that caused it

 

Your alt is good, the issue is the battery isn’t holding a charge.

A good battery should show 12.7- 12.8 after sitting over night. You’re only showing 12.3, and 12.5 right after a charge.

12.2 - 12.4v 20 min after a charging cycle indicates half charged.