Can't get my battery to read 13Vs, stuck between 10-12 (Page 1/2)
Threedog SEP 18, 02:29 PM
Battery reads 12 volts when running, and 11 volts with the A/C on (12 volts when off), this test performed with the in car gauge and a multimeter at both the alt and the battery. However, the car never dies and the battery stays charged. (I have been driving it regularly for over a month with 0 issues, including long trips).

I have a 3800 installed.

Never had this problem until the alignment shop jumped the vehicle from the alternator positive terminal (they didn't know I had relocated the battery to the front).


Things I have tried/checked:

- New alternator
- New Battery
- Connections from battery to ground and battery to starter have not changed and are still good
- Rebuilt the positive wiring from the starter to the peg under the C500 connector
- Rebuilt the cable from the alternator to the peg under the C500
- Check the alternator plug, red and gray wire (plugging into pin 35 and 62 of the PCM, respectively), are still showing good connection.
My questions are:

- Am causing any damage running at 11-12 volts instead of 13-14?
- What else could be causing this!?
Dennis LaGrua SEP 18, 05:14 PM
Measure the voltage of the battery with the engine off. A fully charged battery should read about 12.6 Volts. When first started with everything off it should read about 13.5 volts and that could go down to about 12V when running. It is common for charging voltages to vary when large loads are placed on the charging system like with headlights/tail lights and A/C Clutch engaged but it really shouldn't go to 11 V often unless the battery is weak.

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Threedog SEP 18, 11:10 PM
Yeah that’s the problem though. I know what it should be, and it won’t read that.

It reads 11ish when off, 12 when running. Brand new battery and alt didn’t change that.

I can trickle charge the battery to get it up to 12v when the car is off. But it goes right back to 11 after one drive.
skywurz SEP 18, 11:17 PM
Have you tried a different meter? Maybe your multimeter is defunct. On trickle it should be over 12
Patrick SEP 19, 04:48 PM

quote
Originally posted by Threedog:

It reads 11ish when off...



Way too low.


quote
Originally posted by Threedog:

I can trickle charge the battery to get it up to 12v when the car is off.



Something is definitely funky. As Dennis stated above, a fully charged battery should be 12.6 volts. Have you tried another meter as skywurz has suggested?

[This message has been edited by Patrick (edited 09-19-2021).]

theogre SEP 20, 01:07 PM
Fresh Fully charge battery is 12.6 to ~ 13v. Sit a day should still be ~ 12.6 or more. (ECM etc pulls power but not enough to drain more in a day.)
Alt running should be 14-15v ("Perfect" is 14.7v.)

Get another meter. Most so if is cheap/free from HF and others.

Better. Get a "small" meter w/ DC Amp Clamp.
If you have Battery Leaches this will find them w/o cutting wires etc.
Example: https://www.amazon.com/Uni-...itance/dp/B00O1Q2HOQ

(Can get bigger DC Amp Clamps but many don't read below 1a.)

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(Jurassic Park)

The Ogre's Fiero Cave

reinhart SEP 23, 03:50 AM
Running car, the voltage is the alternator not the battery. What does your cockpit gauge say when the car is running? If it's low its an alternator or charging circuit issue.
theogre SEP 23, 11:30 AM

quote
Originally posted by reinhart:
Running car, the voltage is the alternator not the battery. What does your cockpit gauge say when the car is running? If it's low its an alternator or charging circuit issue.

That dash gauge like others are often unreliable.
If that is low or bouncing as things turn on/off... very likely have wiring problem(s) like iffy grounds anywhere in the car.

That's Why using Good digital or analog meter reading volts from the battery and alt is first step.
If buying new, Small DC Amp Clamp like example above saves a lot of time looking for battery leaches etc.

notes:
Alt Case and mounting hardware Is the Alt Ground. If they are "rusted" etc will cause problems even if alt output at alt main term and case reads 14-15v.

Alt output low/high can car wiring problem... Main term and big wire in side plug have problems then Alt Reg will have problems.
See my Cave, Alternator Sense
skywurz SEP 23, 12:37 PM
Actually I was half expecting that OP was using the interior dash gauge already and nothing else.
Threedog SEP 26, 02:40 PM

quote
Originally posted by skywurz:

Actually I was half expecting that OP was using the interior dash gauge already and nothing else.



I mean, it did say in my original post "Battery reads 12 volts when running, and 11 volts with the A/C on (12 volts when off), this test performed with the in car gauge and a multimeter at both the alt and the battery. However, the car never dies and the battery stays charged. (I have been driving it regularly for over a month with 0 issues, including long trips)."

(literally the first sentence lol)

Tried a second multimeter, got the same thing. 11.91 with the vehicle off. 11-12 when running. (Again, test performed at the battery and the alt..) I just ordered a third, more expensive multimeter.

Checked all grounds, they are all there and healthy (battery goes to the block and the post on the trunk hinge, I have three ground straps between the engine and the chassis at various points. Edit: I should also add, I ran a set of jumper cables from the neg terminal on the battery over the cabin and to a solid ground on the engine, that didn't increase the reading at all.

I did find out why it dips so hard when I turn the A/C on, the radiator fan motor was burned out and literally started smoking on my drive today. However, that shouldn't impact the reading with the vehicle off/the fan not on, right?
And again, the weird thing is that the car performs fine. It starts right up, the battery never dies, and I can drive it for long periods of time without the battery draining.

[This message has been edited by Threedog (edited 09-26-2021).]