Questions on battery voltage readings

[NeedForGreen]

Try another meter.

For? On a basic multimeter the numbers will always vary.

New battery isnt fully charged when you get it. If you do longer drives on your commute it will get there - or put a charger on it overnight.

The car has parasitic loads when not used, and will drop the voltage over time.
A fully charged battery with NO connection will read about 13.85V
However if connected with a light load will indicate (and this is approximate) 12.x V

While driving, esp. after starting it should read 14.7 as its being charged.

Once up to fully charged, you may see it drop, esp under acceleration. Not 100% about the mustangs, but others cars I've had its an adaptive process for the car to not charge while accelerating to get you another 10hp ish while the alternator field isnt loaded. It charges more on decel (eg downhill),

The Odessey, being AGM is a curiosity to me, as AGMs in general have different charging needs, esp. in a marine battery. Not being able to set the chemistry of the battery in use often overcharges and 'dries out' an AGM on a traditional flooded charger setting.

The primary benefit of AGM is its construction and able to take a pounding, esp in a small boat on a day with lots of waves. Less an issue in a car with a suspension. Then there is the easy release of high current, which make them popular with the big audio crowd and sharp bass transients.

So it being a car battery ...... I'm thinking hmmmmm..... I gotta believe its designed for a standard car charging system. But??? dunno.

Hope that helps

I can recommend using a conductance type battey tester to show charge AND health of the battery, and most also have a mode to check the alternator ..... though a quick check is to see 14.7v at the battery when charging. see link for EG. they are not much $

https://www.amazon.ca/100-2000-Automotive-Cranking-Charging-Analyzer/dp/B08HXXKS24/ref=sr_1_6?crid=3PZA2SN4HE0ID&keywords=battery+analyzer&qid=1643673261&sprefix=battery+analyzer,aps,131&sr=8-6

I charged the new battery before even swapping it out. It only took an hour with a 10A charger so it was pretty much charged.
I've read a bunch got the Odyssey and love it, but no idea how their voltage looks like. A lot go with the XS Power D4700 which is also an agm battery. I've read Odyssey's are designed specifically for high temperatures which was another reason I went that route.

I actually did order a simular tester which will be here tomorrow. I'll see how that goes.

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[ice445]

I just dropped in the same Odyssey 96R that you have in my car. I'll watch the voltage as I drive home today. I did actually do the proper BMS reset with a scan tool though, so my results might be different.

So, on a 15 mile trip, mostly highway, with a cold start and 28F ambient temps, my voltage stayed at 15.2 the whole time while driving, and dropped to 14.5 while idling. Seems normal to me for cold weather. I suspect if I had driven long enough I'd have seen behavior like yours, where it wasn't doing much other than meeting the demand the car is putting on it. I see you're in FL so there's likely nothing wrong.

 

[NeedForGreen]

I just dropped in the same Odyssey 96R that you have in my car. I'll watch the voltage as I drive home today. I did actually do the proper BMS reset with a scan tool though, so my results might be different.

So, on a 15 mile trip, mostly highway, with a cold start and 28F ambient temps, my voltage stayed at 15.2 the whole time while driving, and dropped to 14.5 while idling. Seems normal to me for cold weather. I suspect if I had driven long enough I'd have seen behavior like yours, where it wasn't doing much other than meeting the demand the car is putting on it. I see you're in FL so there's likely nothing wrong.

Thanks for letting me know.
The one thing that does concern me is all of the negative reviews I have found on Odyssey batteries after the fact. A lot complain about them only lasting a few months or not holding charges.
Their customer service blows from what I've read too. A small group, but still concerning. I did send them a question.
I'll see what my tester shows later when it arrives, but do question if the battery is the issue. There are people who say what I'm seeing is completely normal and is the bms kicking in. Just odd I've never seen voltage change when driving.

 

[NeedForGreen]

This is what Odyssey told me.
I did check my battery with my cheap multimeter this morning with the car off after the car had been sitting since yesterday afternoon and it's reading 12.8/12.9 so normal and it's holding. Haven't started it yet. I'll see what the readings say with the new tester.

 

[ice445]

Thanks for letting me know.
The one thing that does concern me is all of the negative reviews I have found on Odyssey batteries after the fact. A lot complain about them only lasting a few months or not holding charges.
Their customer service blows from what I've read too. A small group, but still concerning. I did send them a question.
I'll see what my tester shows later when it arrives, but do question if the battery is the issue. There are people who say what I'm seeing is completely normal and is the bms kicking in. Just odd I've never seen voltage change when driving.

Every product will have some negative reviews. Enersys makes AGM's for a few of the big parts stores, and typically they do a good job. I've had a few over the years from advance auto and they always did me well.

The only thing that's odd is you aren't seeing a physical meter reading of 12.8 ish after a good drive.

 

[NeedForGreen]

So my new tester showed the battery is normal.
Showed 14.8 no load. 13.6 with load.
Crank test is normal, but charging test came back high so looks like my alternator.

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