Questions on battery voltage readings

[NeedForGreen]

I just replaced my stock battery with an Odyssey AGM performance one. I did a bms reset (non forscan way posted on here and let the car sit for 8 hours).

With the stock battery the voltage on my dash would always read a consistant 14v until recent when it started showing 11.5v.

With the new battery it will start at 14 to 14.5 then drop to as low as 12 when driving. At times it will bounce back up to 13 or 14. Is that normal?

If my old battery would be consistant why is the new one showing different numbers at diferent times?

I used my multimeter to check the battery and with the car off it shows 12/12.5v and on 13/13.5 so I assume the battery and alternator is fine.

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[KeyLime]

I think that's normal. Instead of holding a fixed voltage the BMS drops the voltage during low demand. I suspect it's one of those tricks to shed some load on the engine and squeeze another fraction of an mpg out of it.

Having said that I seldom if ever see less than 14 or 14.5 volts on my Mustang. But my Nissan Frontier's voltage is all over the place. Maybe it's the crap Ford factory battery.

 

[19gtaz]

I just replaced my stock battery with an Odyssey AGM performance one. I did a bms reset (non forscan way posted on here and let the car sit for 8 hours).

With the stock battery the voltage on my dash would always read a consistant 14v until recent when it started showing 11.5v.

With the new battery it will start at 14 to 14.5 then drop to as low as 12 when driving. At times it will bounce back up to 13 or 14. Is that normal?

If my old battery would be consistant why is the new one showing different numbers at diferent times?

I used my multimeter to check the battery and with the car off it shows 12/12.5v and on 13/13.5 so I assume the battery and alternator is fine.

Did you lock the doors before you let it sit for 8 hours?
My voltmeter reads as low as 11.5 volts when sitting with ignition on, which is way lower than the actual battery voltage.

 

[NeedForGreen]

Did you lock the doors before you let it sit for 8 hours?
My voltmeter reads as low as 11.5 volts when sitting with ignition on, which is way lower than the actual battery voltage.

I did.

 

[19gtaz]

I did.

I would drive it for a while and report back. I think it will normalize, but would like to know if it does.
I'm still on the original battery, but I'm going to AGM when this one gets a bit older. I think 12.0 is a bit low for sitting off. I bet that goes up after a few days.

 

[NeedForGreen]

I would drive it for a while and report back. I think it will normalize, but would like to know if it does.
I'm still on the original battery, but I'm going to AGM when this one gets a bit older. I think 12.0 is a bit low for sitting off. I bet that goes up after a few days.

I actually fully charged the battery once I got it, but it was pretty much already charged. Been driving it for a few days.

 

[19gtaz]

I actually fully charged the battery once I got it, but it was pretty much already charged. Been driving it for a few days.

Did you measure the battery directly on the battery terminals? 12.0 is low, maybe check with another meter. Is it starting ok with no drag or hesitation?

 

[NeedForGreen]

Did you measure the battery directly on the battery terminals? 12.0 is low, maybe check with another meter. Is it starting ok with no drag or hesitation?

Yea I did. That's what the readings I posted above were. The multimeter showed 12/12.5v and on 13/13.5.
It starts right up. Maybe it just needs more time to adjust.

 

[19gtaz]

Yea I did. That's what the readings I posted above were. The multimeter showed 12/12.5v and on 13/13.5.
It starts right up. Maybe it just needs more time to adjust.

I don't understand what you mean by 12/12.5v it's either one or the other, 12 or 12.5.

 

[NeedForGreen]

I don't understand what you mean by 12/12.5v it's either one or the other, 12 or 12.5.

I mean it varies beteen 12 and 12.5. It doesnt stick exactly on one number. 12, 12.3, 12.4, 12.5.

 

[19gtaz]

I mean it varies beteen 12 and 12.5. It doesnt stick exactly on one number. 12, 12.3, 12.4, 12.5.

Try another meter.

 

[Zathras]

I've got 3.5 years on the OEM battery, although not a whole lot of mileage, and it seems like it's cranking slower lately. I also notice that when I drive, it's always showing a high voltage (14.4-14.7 V) which suggests to me that the charging system is working really hard. When the car was newer, the indicated voltage would drop into the 13 or 12 V range as you drove and the battery neared a full charge, but now it never drops below 14.2 V even on a longer drive. Would it be safe to say that this battery is nearing the end of its life?

 

[nustang]

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-Auto...73261&sprefix=battery+analyzer,aps,131&sr=8-6

 

[19gtaz]

I've got 3.5 years on the OEM battery, although not a whole lot of mileage, and it seems like it's cranking slower lately. I also notice that when I drive, it's always showing a high voltage (14.4-14.7 V) which suggests to me that the charging system is working really hard. When the car was newer, the indicated voltage would drop into the 13 or 12 V range as you drove and the battery neared a full charge, but now it never drops below 14.2 V even on a longer drive. Would it be safe to say that this battery is nearing the end of its life?

Your battery is showing its age. You are in a warmer temperature which doesn't help.
That doesn't mean it's going to die next week or even next month, it's just an indicator.

 

[nustang]

Your battery is showing its age. You are in a warmer temperature which doesn't help.
That doesn't mean it's going to die next week or even next month, it's just an indicator.

you need this:
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


Oh... and when testing battery health - disconnect the battery so its the only thing in circuit.

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