Battery, Alternator, or VR?

[phishtaco]

Help me figure out which thing to change.
Dead battery
Jumper cables, let it charge for 5-10
Jumped it
Pulled the cables and let it idle for about 15 minutes
Tested alternator “charging high” loaded 16.22V unloaded 17.4V ripple 41mV
Shut it off and no charge no start

Battery test results after idle and shut down in the picture.

Battery is about 2 years old 2024
Alternator at least 22 years old
VR at least 22 years old.

I feel like it is just the battery but it was replaced in 2022 and 2024. Obviously this is not driven too much. Maybe 1000 miles between August and October of 2025.

 

[igotta40]

What is your amp meter on your gauge panel doing?

 

[Engineer8000]

16-17 v seems kind of high.

 

[phishtaco]

What is your amp meter on your gauge panel doing

Didn’t pay attention.

 

[pb4ugo]

Isn't the v/r adjustable?

 

[cruisermatt]

if you can get 16v then your alternator is perfect.
Your VR should step that down to 13.5V ish.

You can definitely hurt a battery overcharging it and/or letting it sit for extended periods.
Get the battery tested regardless - they can show 12V but have dead/shorted cells and no CCA’s.

On a 50ish year old vehicle wiring you really should be checking every circuit for resistance, corrosion at connectors, etc.

Diag, diag, diag. No guessing or assuming allowed.

 

[charliemeyer007]

I think 14.4 is the high end for charging a lead acid 12 volt battery. Volt meters can very some, almost nothing reasonably priced is actually calibrated. You might be able to adjust the VR. I would invest in a new one and alternator now while you can get them. I also put new 2/0 copper cables for the battery to starter and engine ground - cranks over much stronger now.

Batteries are crap these days. Most die soon after the warranty is up (by design). You let them go flat like 5 times and its dead.
A $50 load tester can be handy.

 

[phishtaco]

I think 14.4 is the high end for charging a lead acid 12 volt battery. Volt meters can very some, almost nothing reasonably priced is actually calibrated. You might be able to adjust the VR. I would invest in a new one and alternator now while you can get them. I also put new 2/0 copper cables for the battery to starter and engine ground - cranks over much stronger now.

Batteries are crap these days. Most die soon after the warranty is up (by design). You let them go flat like 5 times and its dead.
A $50 load tester can be handy.

Actually have an alternator and new VR along with battery cables.

 

[phishtaco]

I’ve tinkering with this here and there.
Warrantied a new replacement battery
Changed VR
Added new battery positive and ground cable to motor. This has been my only ground from the battery for 20+ years but I have one to go to the frame under battery tray. All cables from the mud vendor forerunner???
Screwdriver sticks to alternator
Battery before start sitting for 24 hours 11.79V
Battery full choke at start 13.25 V 14.9 at alternator B lug
Battery at idle after warmed up 12.53V 13.1 at alternator B lug
Says it’s charging normal. Think I’m good to go?? Still need to clean up some grounds I’m sure because headlights and heater are not currently working. Open to any suggestions or comments, ih8electricals

 

[sggoat]

Would still like to see what the ammeter is showing--voltage doesn't tell the full story here. With a battery at 11.8 volts at start, you should see the ammeter jump up to almost pegged at 30(it may wiggle around a bit as the VR adjusts) while at idle, the ammeter should gradually drop back to essentially zero charge after several minutes--tells you the batt is charging and thVR is working

 

[charliemeyer007]

Ammeter tell the whole story about doing work. When my 30 A alternator dies I'm going with a GM 1 wire 105 A unit. I will change to a volt meter as my indicator of battery power. Not as accurate but quick and easy to get the job done vs. re-wiring the system, figuring out the correct shunt/meter. Hopefully by then I'll have my duel battery system installed. It will be a big manual switch on the positive terminal for 1, 2, or both big batteries.

 

[phishtaco]

Would still like to see what the ammeter is showing--voltage doesn't tell the full story here. With a battery at 11.8 volts at start, you should see the ammeter jump up to almost pegged at 30(it may wiggle around a bit as the VR adjusts) while at idle, the ammeter should gradually drop back to essentially zero charge after several minutes--tells you the batt is charging and thVR is working

Just did same basic tests 24 hours later. Same basic results. I did watch the Ammeter. It was dead center before starting but it only moved a very little bit to the right the entire time. Ran choke full for a few minutes then idle for few more then did the alternator test at 2500 rpm. Ammeter didn’t move much at anytime.