Battery or Alternator?

S

slimatic

New member
So a few weeks ago my truck wouldn't start and I needed a jump, this was right after driving it for a good 30 mins, which I figured was not good.

Since then its been happening more frequently and now i'm at the point where it needs to be fixed. I just need to figure out if its the battery or alternator.

Last night was the worst. While I was driving on the highway my power shut off. Interior lights and radio went out for a moment before returning.

Also when I got home and opened up the door the interior lights didnt turn on right away and when they did they dimmed really fast.

So i'm leaning towards it being the battery, but still not positive. Anyone?
 
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I would take your alternator & battery in for testing. Make sure your battery terminals are cleaned just for good measure too.

Sorry about such a general answer, but it's all I can think of.
 
I was going to say most National Auto Parts stores offer free testing and most can do it on the car. I know the Autozones in Cali can roll a cart out to the vehicle and hook up a few things and being able to tell you what is wrong as far as battery or alternator all FREE, of course that is in the hopes you buy replacement parts from them.
 
If you are losing power while driving, then you have a short, and open, or a bad alternator. You can drive without a battery, you just can't start without a battery.

I agree, any national chain should diagnose it for free.
 
I agree w/ the other folks...take it to Kragen or those Auto Shops and they will test your Battery & Alternator for free.

Sounds like an alternator.
 
My suggestions:
1) Load-test battery. Make sure it has full charge if it passes.
2) Clean both battery terminals, both posts and all accessible grounds and the spot where they hit the frame.
3) Inspect cables carefully--any signs of corrosion under insulation or bolt-on repair-type terminals means time for new cables. If they are just old and ugly get new cables. Get them good and tight and put Vaseline on the posts when you put battery back.


Then report back--really need to have good starting current available to do any intelligent troubleshooting.To me, your symptoms sound more like cables/connections, battery, alternator--in that order, so I'd wait on the alt. test. If you want to do the drive-in diagnostic, fine, but don't pull it. [I don't trust those autoparts store on-car drive-in diagnostics, anyway. Test is worthless if you don't isolate the component from the car wiring, IMHO. Of course, Kragen will cry itself to sleep if they sell you an alt. when your problem was a loose ground.]
 
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Nelsonmd said:
If you are losing power while driving, then you have a short, and open, or a bad alternator. You can drive without a battery, you just can't start without a battery.
Click to expand...

Problem is, he said night. So lights on, maybe other loads. Highway, but cruising at low RPM and yeah marginal battery can do that. So I voted cables/connections, then battery, then alt. To me, alt. is least likely for intermittent fail, but certainly a possibility. That's why we troubleshoot.
 
How many miles on the 4Runner? You'll go through 2 or 3 batteries in 100k miles, and then one alternator.

BTW, if it's the alternator, don't buy a new one. You can have them rebuilt at an Alternator & Starter shop (check your phone book) for around $100, and everything's new except the case.

Pick a store that you would buy a new battery at, and ask them to test the battery. I always remove the battery from the vehicle and carry it in. They can test it, and see if it's accepting/holding a charge. If it's bad, buy a new battery. If it's good, bring it back home and pull the alternator for a rebuild.
 
LakeRunr said:
How many miles on the 4Runner? You'll go through 2 or 3 batteries in 100k miles, and then one alternator.
Click to expand...

While this my have been your experience, I wouldn't preach it as gospel.

Some people drive 35,000+ miles a year. I've seen the OEM Panasonic battery last for ten years or more so..........
 
You can drive with either just an alternator or a battery. Just not too long on a battery as most circuits will shut down under 10.5V for safety. I would put my money on a bad alternator. I just replaced two in one month. The original was a Duralast and I replaced with a Duralast. DO NOT get a Duralast! I replaced it with one from Advance Auto and like it more, they also price matched to the cheaper Duralast. I'd rather fork out the $130 and have the warranty than to get one rebuilt. Good luck, this is definitly an easy DIY project too.

Here's a simple alt test: disconect charging cable from alt and start it up. You should be getting about 14 +/- 0.5 Volt out.
 
mom said:
In some cars, that's injurious to the electronics. dunno though if the Toyota is one of them.
Click to expand...

I agree with Mom. Page CH-1 (Charging) of my '99 4Runner FSM says on the front page in bold: "Never disconnect the battery while the engine is running." I was told long ago that the internal regulators will burn themselves up trying to charge a battery that isn't there.

No problem on a 1955 Ford F-100 with a genny. But I wouldn't risk my Denso alt. Get a volt meter and a load tester, for Pete's sake. If you see ~13.7 volts or more on a voltmeter, alt is working. But to be sure, the load tester will put it under load.

A fully charged battery should give 12.7 to 12.9 volts at toom temp. Load test it to check cranking amps. It all takes two minutes.
 
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The battery is almost like a shock absorber of sorts. The Alt will continue to charge it and the car will pull the power it needs off the battery. The Alt output voltage varies by RPM (faster the engine turns the more voltage and it's regulated (usually to a max of ~14-14.5V) by a voltage regulator. The reason you don't want to drive without a battery is because the systems want a constant voltage and driving without it will change voltage going to the car if you're directly off the alternator. The Alt has to produce higher voltage than the battery. That's how a DC system charges.... difference in voltage : higher going to lower.

However, if you have the car idling with lights on and you unhook the battery, your only power source is the alternator. At that point, if it dies or goes very dim, the alt isn't putting out enough power or the voltage regulator on it is bad.

The easiest thing to do is go to an Advance Auto Parts or anything like that and have them test it. It's free, it's fast, and it's the safest thing to do. Since you were driving and stuff started cutting off, the first thing on my mind is that it's the alt, but you need to have it checked to be sure.
 
LakeRunr said:
How many miles on the 4Runner? You'll go through 2 or 3 batteries in 100k miles, and then one alternator.
Click to expand...

notrayray said:
While this my have been your experience, I wouldn't preach it as gospel.

Some people drive 35,000+ miles a year. I've seen the OEM Panasonic battery last for ten years or more so..........
Click to expand...

Point taken. I put 100k miles on a truck in 10 years. My last one being a 3rd gen 4Runner. What I should've said was that you'll go through 2 or 3 batteries (including the original) before you go through one alternator...on average.
 
Sorry to piggyback on this thread, but I have no post count and can not start a new thread yet.

I have an 06 4Runner V6

I believe I have some sort of excessive draw on the charging system causing my vehicle to destroy altenators.

I do not believe that it is a typical parasitic draw because it doesn't show itself when the key is off and doesn't drain the battery with the key off.

It seems to drain, or I guess tax, the charging system while the vehicle is running.

How do you find the culprit with the power on?

I can add more info as I go,

On my third alternator within a week, and replaced the battery with the second alternator.

Third one is melting in the back of the alternator like the rest have, including the OEM one.

Battery at 12.6V resting
Jumps to 14.+ right after starting.
After starting it drops down about .01V per 2 seconds till levelling out around 13.6V.
If I accelerate say above 2500rpm range I get 12.V
 
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Mantilgh said:
Battery at 12.6V resting
Jumps to 14.+ right after starting.
After starting it drops down about .01V per 2 seconds till levelling out around 13.6V.
If I accelerate say above 2500rpm range I get 12.V
Click to expand...

This all sounds pretty Ok until you read that last line. That one is a problem. Strange.

This is the 3rd gen section of the forum, have you tried the 4th gen section too?
 
Mantilgh said:
Battery at 12.6V resting
Jumps to 14.+ right after starting.
After starting it drops down about .01V per 2 seconds till levelling out around 13.6V.
If I accelerate say above 2500rpm range I get 12.V
Click to expand...
I agree that 12V at 2500RPM is way wrong. Volts at 2500RPM should be the same as at 800RPM or 3500RPM.
Voltage runs higher (like 14.3) in cold temps, then lowers in hot temps (like 13.7).
You are in to a shell game of what is killing what.
One scenario:
You MAY have a situation where a battery went bad, and then the bad battery killed the alternator; replacing the batt at that point didn't fix the [now malfunctioning]alt so the alt killed the second battery, and so on. Get the alt tested at idle and 2500 RPM, and prepare to buy another alt and/or another battery.
 
Smack your alt with a hammer. If it now charges throughout the entire rev range it’s time to replace your brushes in the Alt. Your voltage regulator could also be going bad.


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