Charging system problems

Ok so here goes. I had an old age in the truck for almost 6 years. It finally went. Had it tested at advance auto and they said a bad battery so got a new agm all was fine for a few months then since my truck sits for days I went to start it up and nothing. Not even an attempt to turn over, Using Jump pack starts right up.No new draws put in the system. Ie lights etc. so I’m on my second new battery so I’m thinking it’s not the battery. The truck sits for more than 2 days it needs a jump. Voltage around 7. After I drive it around it charges to about 12.1 -12.3. My thought is a parasitic leak.

so today I take it to my dads shop for a load test and he seems to think it’s the alternator. So now with the truck off it measures at 12.1volts. And with it running it measures 13.7. So my thought is at 171k miles the alternator is not charging the battery fully??

input?

 

Both 12.1 & 13.7 voltages are low. If pops says alternator, he's probably right. Also you may have something draining the battery. A parasitic draw test should be done too.

 

Yep. Find it.

 

What’s the best way to find it if anyone has done it

 

Charging at 13.7 is good and when off a battery should read 12.6 (2.1 per cell and there are 6).
What did you not tell us i.e. what have you done/installed recently (new stereo always powered on, winch, offroad lights, new alarm system, etc).
Look for any wires that have insulation cuts.
Animals chewed any wires -pull the plastic cover off top of engine and look under there as that's where they love to live and eat wires.
Other things are bad battery cables/connections and ground battery to frame and block.
Trailer power to 7 pin on bumper issues (there is a fuse so you can pull to verify no damaged wires back there).
Then if all else is OK could be alternator but charging at 13.7 does not point in that direction.

 

I've never done it but saw it done on YouTube. With the key off, doors closed, everything off. Put an amp clamp on the positive battery cable, it should read less than X amps. If it's higher, you have a problem. One at a time pull every fuse, check the amp clamp reading. Amperage will drop significantly when you find the right fuse. Then you gotta trace that circuit to figure out what's causing it.

Sorry, pretty vague, someone will hopefully provide better instructions.

 

Nothing new installed on the truck in over 2 years.

 

Yep amp clamp on a battery cable or amp meter inline between battery post and cable. Look for an excessive amount of draw. Opinions vary but it should be less than 50 milliamps (0.050 amps)

If more than that, start pulling fuses until the draw goes away

Also 12.1 is too low. If it drops to that level immediately after turning off the engine the battery is probably bad

 

13.7-14.2v running

fully charged battery at rest should be 12.6-12.7v

 

so if the alt is only charging while running to 13.7 obv the battery doesnt ever really get fully charged correct? because as soon as you shut f off it reads 12.1. but wouldn't the battery still remain at that 12.1 after sitting for 3 days or so. the battery will drop to 7.3v after sitting for days. does that mean a draw or does it discharge because it never reached full charge at 12.6

 

Maybe. As mentioned it's a bit low on the alt output. But I assume you are measuring at the battery posts. A cable or terminal issue could restrict that measurement. Measure at the alternator to see what it's really doing. And as mentioned, 12.1 is a bit low, but should be startable.

Yes, unless the battery is bad or you have a draw

High odds

Doesn't seem logical. A health battery can sit for weeks at the same voltage it started at.

While you've not added anything new recently, it doesn't mean something hasn't changed. @muddog321 gave a good outline of suggestions.

 

Charging voltage is temperature dependent, most Toyota's I've seen run anywhere from 13.2v when it's hot to over 14v when it's cold.
My truck goes to 13.8-14.2v on a cold start and comes down to 13.2-13.4v once it warms up.

The 12.1v engine off voltage is concerning, either the battery isn't fully charged or it has a dead cell. Standard lead acid batteries are 12.6v at full charge, AGM batteries are typically slightly higher.

One way to see if it's the battery or not is to leave the battery disconnected when you let it sit, if the battery still dead when you come back to it you have a bad battery.

 

so drive with it in the truck to charge to whatever i gets to, measuer it, pull it from the truck and let it sit to see if it drains down?

 

If it's that low it would be best to charge it with a battery charger but yea charge it up, leave it unhooked, and see if it goes dead sitting there.

 

If you replaced the battery with an AGM, I think there is a mod you have to do to charge it properly. AGM's need like 14.0 to 14.7 volts to charge properly. 2nd gens have a physical mod (I am sure you can find it here somewhere), 3rd gens have to have the ECU updated.

 

i thought as much but i have been running an agm in some way shape or form for over 7 years now first was a yellow top and each one has been fine without said mod, but am gonna look nto it more

 

Charge the battery out of the truck, let it sit overnight and measure the voltage.

 

also noticed that company is out of stock if i wanted o gie it a try any insight from anyone, i hear there is a chevy or ford fuse that you can use that does the same thing for AGM batteries in our trucks

 

Gen 2 and after 2 AGMs over 8 years now and never did a mod and never a problem and live in hot climate so lots of stress.
5 years on first and still fine but became a spare as I use boat ramps and camping out.
But I don't run big amps or refrig so never highly discharge them, on purpose.

 

Yeah, its seems like most people don't do the mod and don't have any issues. Here's a big thread on the mod, though: https://www.tacomaworld.com/threads/the-northstar-agm-battery-voltage-booster-upgrade.604478/