Long story short, during a 45 min drive, my battery light came on and went off after about 15 seconds. Got to my destination, parked the truck and it didn't start 5 hours later. I noticed the wipers seemed a little slow on the way but I attributed that to it being 2 degrees F out.

I got a jump and it fired up. I drove it 45 minutes back home without a problem. After sitting for another 8 hours, it cranked just fine. Shortly later, I left and after 10 minutes on the road, the battery light comes back on. I turned around and parked it in my garage.

Also, my battery is less than 5 months old. I let the truck sit for 2 hours and just checked the voltage. Battery was 12.04v. I started it and got a reading of 13.4v at idle.

The belt looks good and the alternator looks pretty clean (no oil leaks etc on it).

I don't see how the alternator could be the issue since the battery is getting a charge. Don't alternators either work or not work at all? Maybe a grounding issue?

Thanks in advance.

No. Alternators don't work or not work at all. They go out. Sometimes they work, sometimes they don't.

Could be a loose ground, could be the temp, could be your alternator.

Pull it and get it tested, see if that's the problem.

how old is the alternator? from the sound of it, you may have a bad alternator or bad connection at the battery terminal or corroded battery wires.

After you fix/replace the battery, upgrade your battery negative to chassis ground wire to 4 G.

That should bring your voltage up to 14.2.

Thanks. I'm going to pull it tomorrow and check the grounds. I'll check the brushes also.

I like the way you specifically said "fix/replace the battery".

I tend to agree and a shorted battery can make your alternator do funny things as well as damage it.

Check your battery first by starting the truck for a couple of minutes then shut down and immediately disconnect a battery post.
Don't matter which post, it's to stop parasitic drain from electronics in the truck. Test the voltage with a DVM confirming it's 12.8 vdc.

If it's not, put a trickle charger on it and check it again is a few minutes and get that voltage up to 12.8 then pull the charger off.

Wait 1 hour then check again the voltage and if it's dropped to 12.5 or less, not good !

Investigate further on the battery via load test or just replace it.

This is $0 cost troubleshooting and really helps narrow out your choices of possible problems.

All of the above is good stuff. FYI Your voltage with the truck on should be above 14V.

13.4v is low, mine reads 14.3v when running. at idle its still around 13.9-14v

Starter maybe?

good info, thanks!

Not sure if you are saying that about 3rd gens only or in general. I don't agree that voltage should be above 14. Many vehicles' voltage regulator won't allow it, and sometimes getting high voltage is an indicator of sulfation in the battery. And some vehicles do get above 14 all the time.

Battery voltage is a very complex subject, there is no absolute correct voltage on 12V systems. There are just too many variables.

Ahhh it's pretty agreed upon that a 3rd gen 4runner should be above 14.0 when the engine is running.

Well I agree that mine is at 14.2 with the engine running and no load. heh

My voltage was about 13.6 when engine running at 2000 RPM for years.

My batteries would "go bad" after 2 years and i thought I had a drain issue.

Finally I upgraded the big-3 and now I'm seeing 14.2 at the Scanguage and my battery is no longer dead when sitting after a few days.

I think my system wasn't charging properly and the big 3 helped.

I fight that battle on the RV. 5 batteries, 4 of them 6V. Converter, Inverter, Generator, Alternator, continuous duty solenoids, and monitor panels. I have voltage drops all the time, every connection is a theoretical drop, but with so many cables and corrosion it's a not stop parade of issues. I run 2 batteries in my FJ62 with a home made isolation system and a 95 amp alternator, I had trouble with Optimas, but with just cheap batteries it seams to work fine.