01 E350 V10 wagon charging issues

[packmule]

I'm having some issues with my van's charging system. It's an '01 E-350 RB wagon with the V10 and the auxiliary battery option. Here is what I know...

1. Main battery age unknown and seems to be pretty weak. After 30 minutes of engine off dome light usage, it fails to start. Battery voltage is right at or below 12v at that point.
2. Frame mounted auxiliary battery age unknown. Have not tested voltage at battery.
3. Idle charging voltage with no load is 13.2-13.6v... in spec, but on the low side
4. 2000 rpm charging voltage never exceeds 13.6v
5. Loaded (a/c, radio, interior and exterior lights) charging voltage is 12.4-13.0v, below spec.
6. Basic visual inspection of battery cables and terminals looks good
7. No parasitic draw... 13 mA with everything off
8. Serpentine belt replaced last spring, tensioner ok, no unexpected belt noise

I suspect that I need a new alternator based on the low loaded charging voltage, and probably a new main battery. Does that seem reasonable or are there other tests I should be running to isolate the issue? I assume the aux battery is old and needs to be replaced, and that keeping the old battery in the charging circuit can create issues. Should I just remove the old battery and secure and insulate the aux battery terminals until I'm ready to set up the van to tow a travel trailer?

 

[mikracer]

I would get the battery load tested before going through with changing out the alternator.

 

[packmule]

I would get the battery load tested before going through with changing out the alternator.

Thanks. I should have added that I did a crude engine off load test, turning on the headlights, interior lights, radio, and hazards... battery voltage dropped to 11.9-12.0v in a minute or so. It still started at that point, but it wasn't a strong start.

I just got back from Auto Zone and they load tested the battery and it passed. The alternator failed the diode test, so I plan to replace it tomorrow. I still question the battery. Also, I'd appreciate any thoughts about dealing with the aux battery. Is removal a good near-term option if I don't plan to tow a travel trailer right away?

 

[bknudtsen]

If you can't afford to replace both batteries and the alternator, then I would replace the main battery, the alternator, and disconnect the second. If it is dead, it will absolutely draw down on your new battery and eventually burn up your alternator as well. For clarification, is your second battery isolated from the main, or just wired in parallel?

 

[packmule]

If you can't afford to replace both batteries and the alternator, then I would replace the main battery, the alternator, and disconnect the second. If it is dead, it will absolutely draw down on your new battery and eventually burn up your alternator as well. For clarification, is your second battery isolated from the main, or just wired in parallel?

I think the second battery is isolated. It's the factory aux battery option that I believe only powers the trailer connector. I won't be towing for a year or two at least, so I plan to replace the main battery and alternator, and temporarily delete the aux battery. Thanks for the help...

 

[packmule]

I replaced the alternator and main battery as well as deleted the aux battery the other day. Charging voltage is now ~14.3 and everything looks good. The aux battery I removed was the original Motorcraft part from 2001, with a resting voltage of 8.2v!! :Wow1: The aux battery box is a bit rusty, so I need to clean up and repaint it before I reinstall it.

 

[bknudtsen]

The aux battery I removed was the original Motorcraft part from 2001, with a resting voltage of 8.2v!! :Wow1:

That would do it!