Ever see a Battery Voltage Go UP after resting

[mobiledynamics]

Tinkering with the charging system...

Battery charged, rested overnight, V read 12.7
3/4 Mile Drive. Reads 12.4
8 Mile Drives, 3-4 Ignition Cycles later. V on Battery still at 12.42

Walk back to the battery 2 HRS later. Engine has not been on, etc. Battery is reading 12.7

Never seen a suspect battery go UP in V while standing.
Anyone have any insight

 

[Showkey]

Sounds like you’ve got battery and or charging system issues.
Is the voltage measuring device reliable and decent quality ?

Type of Vehicle ?

Normal charging voltage is 13.5 to 14.5 for most vehicles. Modern vehicles the charging system is controlled by the ECU.
Normal fully charged static or resting voltage 12.8 volts.

 

[mobiledynamics]

Typing this on the phone but during the test drive, alt voltage seemed in check. I do see a momentary dip on decel down to low 12’s but it drops and then climbs back up.

Just wasn’t expected to see the V go up after walking back to it 2 hrs later

 

[rlitman]

Yeah, batteries can do that. Take a battery off float and put a discharging current on it. The voltage will quickly drop, and then slowly rise back up again. The chemistry reacts more slowly than you'd expect. DC capacitors have a similar issue with polarization.

Did you have it tested with a Midtronics?

 

[mobiledynamics]

No idea what they used at AutoZone. They went through the screen, chose battery type and then how many CCA. The tester reported (battery replacement) but aside from that, I have no idea how the tester determines it or how accurate their tester is.

Same tester also ran on alternator. They said it checks out fine.

Still diagnosing. I feel like it's gotta be the ALT but since I started troubleshooting and looking at the V real time, it looks fine when I'm monitoring. However, even with a GOOD battery I have and put it in the same vehicle, I'm still getting gremlins...that sorta point towards the alt. Unless, the alt is dropping the voltage in a nano-second and I'm not seeing this.

 

[Sevenhills1952]

Yeah, batteries can do that. Take a battery off float and put a discharging current on it. The voltage will quickly drop, and then slowly rise back up again. The chemistry reacts more slowly than you'd expect. DC capacitors have a similar issue with polarization.

Did you have it tested with a Midtronics?

X2 this explanation, I'm electronic tech. and have seen it happen.

Sent from my SM-S320VL using Tapatalk

 

[Oggy]

My experience (tech in the army) is that the battery is 90% of the time to blame. We replaced a couple alternators (2) on a Humveee because we had already replaced the batteries, turned out one of them was bad "out of the box."

Ymmv, I would do a load test on a different machine for the battrry, or, if it's close to time, replace it.

Sent from my Pixel 2 XL using The Garage Journal mobile app

 

[850xpeps]

No idea what they used at AutoZone. They went through the screen, chose battery type and then how many CCA. The tester reported (battery replacement) but aside from that, I have no idea how the tester determines it or how accurate their tester is.

Same tester also ran on alternator. They said it checks out fine.

Still diagnosing. I feel like it's gotta be the ALT but since I started troubleshooting and looking at the V real time, it looks fine when I'm monitoring. However, even with a GOOD battery I have and put it in the same vehicle, I'm still getting gremlins...that sorta point towards the alt. Unless, the alt is dropping the voltage in a nano-second and I'm not seeing this.

A bad battery will drop down when loaded and come back up when no load. Do you have a battery load tester? Basically an element. Hook up and turn switch on and watch needle. If drops to bad battery point then time for a new one.

 

[Vvmvbb]

Sounds like fairly typical recovery effect.

https://en.m.wikipedia.org/wiki/Recovery_effect

Might be a little more pronounced if the battery is stratified (i.e. acid has settled to the bottom, water on top), which I think can happen if the battery sits < ~80% charged for a while or never gets a high enough charging voltage.

Using a multimeter, what is the voltage at the battery with engine running?

 

[Ole Slewfoot]

Or if you have one of those cars that runs some stuff for awhile after you get out, that might drop your 'end of drive' voltage.