Not exactly a BS question, but inspired by faulty battery in my BS.

[biglarrr]

I recently had a very unpleasant experience with my local service department when I found an issue with my 8 month old BS, that was finally traced to a faulty battery. I had to bring my BS in three times, and get various excuses about why they couldn't address the issue.
I finally called Ford Support who put me on a conference call to the dealership.
Long story short, they finally replaced the battery, after I turned in a spreadsheet showing them the voltage drop from day to day when I wasn't driving.

I've continued the daily voltage checks and am seeing something I didn't expect.
The voltage increases on days that I don't drive.
It's a minimal increase, but it's measurable and consistent (average of about .07v per day)
I've heard of and experienced battery rebound on small solid batteries ( alkaline, and nickel hobby batteries) but actually never measured it on a car battery.

Does anyone have a scientific explanation for this - battery rebound(?) ?

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[Mark S.]

Does anyone have a scientific explanation for this - battery rebound(?) ?

It's not uncommon for battery voltage to rebound some after removing a load, but that shouldn't be the case unless the battery load while running is more than the alternator puts out. Have you checked voltage with the engine running?

 

[biglarrr]

It's not uncommon for battery voltage to rebound some after removing a load, but that shouldn't be the case unless the battery load while running is more than the alternator puts out. Have you checked voltage with the engine running?

Yep Alternator voltage is fine, the drain comes after the car is shut off, as you've probably observed if you have a BS, or probably any new car. Lights come on when You open the door, and then fans come on in the headlights to cool and supposed flush moisture from the headlight assembly. I've looked for ways to shut all of this off, but there's nothing in the options to completely eliminate it. The day after I got my BS back with the new battery, I opened the doors to put all of the stuff I took out when I brought it in for service, and the battery dropped .40v in the five minutes it took me to put everything back.
I miss the good old days when you could shut your car off and it would stay off.
Every time I walk by my BS, getting the mail, getting in the other car, looking for something in the garage, it lights up. I need to put a note up by the garage entry to leave my keys in the house.

 

[Mark S.]

I need to put a note up by the garage entry to leave my keys in the house.

Ah yes, reminder notes. Seeing more and more of those lately...

 

[baja_bob]

Are your headlights staying on after you get out of the vehicle? Sometimes I notice that my daytime lights stay on for up to 5 minutes on until I use the keyfob to unlock then relock the doors. I've never had a battery problem though.

 

[biglarrr]

It's not uncommon for battery voltage to rebound some after removing a load, but that shouldn't be the case unless the battery load while running is more than the alternator puts out. Have you checked voltage with the engine running?

update: I thought about your question after my first response, and had to add this.
I don't know and really don't have a way to check whether the alternator is feeding enough amperage to the battery to stay ahead of full charge.
I assume it is only because the running voltage at the accessory port shows 14.4 when the car is running, and - even before the faulty battery was replaced, if I drove for more than half an hour, things would start working that weren't working on shorter drives.
I assume from that, that the battery was charging enough to meet the minimum threshold for those devices to operate.
It was - to put it mildly - a very frustrating issue, and Ford Service was not cooperative at all.

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