Alternator or battery or both?

[Geewhiz]

Hey guys I’m having an issue with my pickup that I need a little help with. Ive never been super savvy with electrical issues.

2010 f150 5.4. Last week everything was just fine, no previous issues with starting. Monday the battery was dead and had to jump 4x throughout the day, I just left it running when I ran errands and it died once when I was in a store. Tuesday morning I went to jump it and as soon as I disconnected the jump pack it died. I did it again and same result, so I drove my other pickup to work. Got a new alternator yesterday evening and put it in and while I was at Napa I had the kid behind the counter test the battery and he said it tested just fine. (Should I trust him or not?)

After installing the new alternator last evening I started it up just fine (with a freshly charged battery) and let it idle but after running for 30mins or so it died again. If I understand correctly, once started shouldn’t it run on the alternator regardless of the status of the battery?

I’m just a bit confused. I think that I likely need a new battery as well but beings as I just got it tested I’m not sure.

Thoughts would be appreciated.

 

[go_deep]

Just dealt with this on my son's jeep. 12.6V on the battery, 688 cold cranking amps, battery passed all tests, multimeter on the alternator showed it producing 14.8V. So it took a few days because everything said it should start, but it acted like a dead battery, sometimes, not every time.
Battery cable was corroded inside on the positive leading to the starter not allowing enough amps to pass through the cable. Replaced, starts every time for the last 10 days since.
Check and clean all the connections to and from the battery first.

 

[SDHNTR]

What voltage is it putting out while running?

 

[Geewhiz]

What voltage is it putting out while running?

I didn’t check it on the old alternator but I will be checking that when I get off work tonight.

 

[wyoguy]

Napa and other parts stores have battery testers, I'd have it tested then go from there.

 

[Laelkhunter]

Napa and other parts stores have battery testers, I'd have it tested then go from there.

He did have it tested at NAPA, kid told him it was fine.

 

[Laelkhunter]

Hey guys I’m having an issue with my pickup that I need a little help with. Ive never been super savvy with electrical issues.

2010 f150 5.4. Last week everything was just fine, no previous issues with starting. Monday the battery was dead and had to jump 4x throughout the day, I just left it running when I ran errands and it died once when I was in a store. Tuesday morning I went to jump it and as soon as I disconnected the jump pack it died. I did it again and same result, so I drove my other pickup to work. Got a new alternator yesterday evening and put it in and while I was at Napa I had the kid behind the counter test the battery and he said it tested just fine. (Should I trust him or not?)

After installing the new alternator last evening I started it up just fine (with a freshly charged battery) and let it idle but after running for 30mins or so it died again. If I understand correctly, once started shouldn’t it run on the alternator regardless of the status of the battery?

I’m just a bit confused. I think that I likely need a new battery as well but beings as I just got it tested I’m not sure.

Thoughts would be appreciated.

How old is the battery? What does the gauge on the dash show?? If the needle to the right, it's charging so alternator should be good, if the needle is to the left, it is discharging and probably the alternator. If the battery is more than 2 years old, probably the battery. If less than 2 years old, should have a pro-rated warranty. I would replace the battery, then watch the gauge on the dash. Needle should be to the right showing charging. and again, if the needle is to the left it's discharging.

 

[Hoghead]

Make sure the alternator is putting out, clean battery cables. The alternator should run the vehicle even if the battery is no good. Just because the alternator is new doesn't mean its putting out. The PCM controls the output of the alternator.

 

[06 SB]

I would have suspected the battery long before the alternator and it is easily tested. A multimeter is your friend. Check battery connections for corrosion and replace the battery. I have had many a battery test good at the shop but do not work. If it is not the battery then something is draining it and will require a lot of investigating to find the culprit.

 

[Geewhiz]

How old is the battery? What does the gauge on the dash show?? If the needle to the right, it's charging so alternator should be good, if the needle is to the left, it is discharging and probably the alternator. If the battery is more than 2 years old, probably the battery. If less than 2 years old, should have a pro-rated warranty. I would replace the battery, then watch the gauge on the dash. Needle should be to the right showing charging. and again, if the needle is to the left it's discharging.

Bought the pickup in December so not sure on age of battery. No gauge on dash. I will put my multimeter to the new alternator after work today to rule that out and then focus on cables and connections.

 

[Geewhiz]

I would have suspected the battery long before the alternator and it is easily tested. A multimeter is your friend. Check battery connections for corrosion and replace the battery. I have had many a battery test good at the shop but do not work. If it is not the battery then something is draining it and will require a lot of investigating to find the culprit.

I decided the alternator was toast when I realized the pickup would die after it was jumped and running. To me that points to the alternator, but I could be wrong.

 

[Laelkhunter]

I would purchase an AGM battery for it (NAPA Legend is what I bought). A little more than the standard lead/acid battery but worth the peace of mind since you have already replaced the alternator.

 

[Fatcamp]

I don't play with tires and batteries. It's my one old guy flex, having new tires and good batteries in all my rigs.

 

[Geewhiz]

Also lights in dash/headlights are dim which makes me think that it’s a battery/alternator issue as opposed to bad cable from battery to starter.

 

[Yoteassasin]

Battery Could be shorting internally if its older than 3 years replace it

 

[Fatcamp]

Bought the pickup in December so not sure on age of battery. No gauge on dash. I will put my multimeter to the new alternator after work today to rule that out and then focus on cables and connections.

Check the outside to see if they taped the receipt to it. I'm guessing they didn't punch the numbers on top. That drives me nuts.

 

[Billogna]

Also lights in dash/headlights are dim which makes me think that it’s a battery/alternator issue as opposed to bad cable from battery to starter.

Do the lights get brighter when you rev the engine?? If so it could be the voltage regulator??...

 

[Yoteassasin]

The manufacture date is on every battery 1/2” circle colored sticker with the last 2 digits of the year . Normally placed on the side. Batteries are so poorly made (every last one of them ) nowadays they are always my first look

 

[ColPenguin]

Check along your terminal cables for any spots where the insulation has worn away.

Leaky battery can wear your cables and then can short out on nearby metal surfaces.

 

[Moby Sculpin]

We have several of those 5.4s at work. Learned the hard way they will NOT run off the alternator. Don’t let that throw you!