Battery Charge Characteristics

[JHZR2]

Posted this via PM to a highly knowledgable member, but figure we will all learn something from this, and I've not found the relevant answer on the net, so want to have it out there.

Parents car uses a group 49/H8 battery, which should be a pretty low impedance battery. Alternator charges, battery voltage rises, seems normal. After it sits though, battery voltage drops fairly rapidly (say overnight) to around 12.2V.

So this could mean high self-discharge (high internal impedance or a soft internal short, right?), or a parasitic load, which could be the case since the car is 16 yo and has 220k miles.

Anyway, what confuses me is the behavior when I put a charger on the battery, in the car. If there was high impedance due to sulfation, or a parasitic draw in the connected electronics in the car, charge time should take forever, especially at low rates (I figure a grp 49 is like 100Ah, so I charged at C/10 since my charger had a 10A option).

What happens though is that it goes from where it was sitting, like 12.2V at 85F, up to well past 13V really rapidly (with the charger stating nearly 100%, and this is a charger I use on my personal batteries of similar capacity and trust). I wouldn't have such an issue with this, but it is charging to "100%" far faster than I would expect from a healthier battery of same group/size, starting at a higher voltage.

So the question is, if under charge, using CC/CV down to a very low current, the battery appears to be "fully charged", but has taken far less Ah than it should have, plus the battery rapidly loses voltage, what is this an indicator of? Sulfation? Loss of lead by some other means? Some kind of soft short that allows for a voltage that is not indicative of a 0V or reversed cell, or what?

Obviously a parasitic load test would be optimal, but they don't have the radio security code with them (were together for Memorial day but don't live really close). So I'm trying to understand if there is a way to discern issues/possible battery conditions from what we are seeing.

Any thoughts on this based upon your experience would be most appreciated.

Thanks and happy Memorial Day!

 

[Warstud]

Originally Posted By: JHZR2
My mother's 97 Plymouth breeze it has no issues - even has original battery


Originally Posted By: JHZR2
Parents car uses a group 49/H8 battery, which should be a pretty low impedance battery. Alternator charges, battery voltage rises, seems normal. After it sits though, battery voltage drops fairly rapidly (say overnight) to around 12.2V.


Is this the same car/battery that has a troublecode?

 

[eljefino]

I share in your search. The exide in my dakota will go randomly near death, "gee I can see the orange glow from the filament in my dome light" bad. Throw it on a 6 amp charge and it's fine an hour later, starts the truck, and won't take any more juice per the charger. It's not a connection as I've yanked said battery and thrown another one in, then replaced it with the first later same day.

I have it broadly narrowed down to "something funky on an internal plate" and if I had to trust the truck, I would replace said battery. They don't do exploratory surgery on car batteries... yet.

Hey maybe we should get 15 year old kids to x-ray our stuff! Lead shows up good, I understand.

 

[brianl703]

Originally Posted By: JHZR2

Anyway, what confuses me is the behavior when I put a charger on the battery, in the car. If there was high impedance due to sulfation, or a parasitic draw in the connected electronics in the car, charge time should take forever, especially at low rates (I figure a grp 49 is like 100Ah, so I charged at C/10 since my charger had a 10A option).


The battery charger assumes that the battery is charged when the current has dropped off to under something like 300mA when the voltage is above 13V.

As you're probably familiar with Ohm's law, you know that a battery which has high internal resistance due to sulfation is not capable of pulling a high charge current like a healthy battery is.

Quote:
So the question is, if under charge, using CC/CV down to a very low current, the battery appears to be "fully charged", but has taken far less Ah than it should have, plus the battery rapidly loses voltage, what is this an indicator of? Sulfation?


Yes, sulfation. I haven't dealt with many sulfated car batteries, but I have about 10 sulfated UPS batteries I need to dispose of...and they act exactly like that. 13V open-circuit terminal voltage, yet you can put a dead-short across them and you barely get a weak spark. Put a charger on them and they won't take any current, acting as though they're fully charged.

 

[JHZR2]

Originally Posted By: Warstud
Originally Posted By: JHZR2
My mother's 97 Plymouth breeze it has no issues - even has original battery


Originally Posted By: JHZR2
Parents car uses a group 49/H8 battery, which should be a pretty low impedance battery. Alternator charges, battery voltage rises, seems normal. After it sits though, battery voltage drops fairly rapidly (say overnight) to around 12.2V.


Is this the same car/battery that has a troublecode?



Nope, the breeze doesnt use a 49/H8 (Euro diesel battery). This is their 96 E300D with 220k, all original (rad, at, alt, etc). So it's quite feasible that something isn't right... But as mentioned, we don't have the radio code right now, so don't want to pull the battery.

The battery is an Exide, which as I understand it may be part of the issue. I have to look at the date code but it is a few years old.

 

[JHZR2]

Originally Posted By: brianl703
Originally Posted By: JHZR2

Anyway, what confuses me is the behavior when I put a charger on the battery, in the car. If there was high impedance due to sulfation, or a parasitic draw in the connected electronics in the car, charge time should take forever, especially at low rates (I figure a grp 49 is like 100Ah, so I charged at C/10 since my charger had a 10A option).


The battery charger assumes that the battery is charged when the current has dropped off to under something like 300mA when the voltage is above 13V.

As you're probably familiar with Ohm's law, you know that a battery which has high internal resistance due to sulfation is not capable of pulling a high charge current like a healthy battery is.

Quote:
So the question is, if under charge, using CC/CV down to a very low current, the battery appears to be "fully charged", but has taken far less Ah than it should have, plus the battery rapidly loses voltage, what is this an indicator of? Sulfation?


Yes, sulfation. I haven't dealt with many sulfated car batteries, but I have about 10 sulfated UPS batteries I need to dispose of...and they act exactly like that. 13V open-circuit terminal voltage, yet you can put a dead-short across them and you barely get a weak spark. Put a charger on them and they won't take any current, acting as though they're fully charged.


Good stuff, thanks.

What has confused me is the comments, even in the charger manual, which indicate that a highly sulfated battery will go through a desulfation cycle and the charger will continue charging until it throws a fault code. I get no faults, in fact, I get the green "ok" light stating that it is done!

So it seems that the charger makers (Schumacher in this case) has given some thought to it and determining when batteries are sulfated... Which keeps me guessing.

 

[brianl703]

I have that same charger and the battery needs to be REALLY bad for it to go into desulfation mode (which I've never had any luck with). Since it apparently still turns the engine over, it's not quite that bad.

I suspect that if you did a load test on that battery, it would not pass, however.

 

[Kestas]

Originally Posted By: JHZR2
But as mentioned, we don't have the radio code right now, so don't want to pull the battery.

Radio codes should be readily available from the dealer. Just prove to them you own the car.

Or you can try the following link below. (I haven't yet tried it myself):
radio codes

 

[JHZR2]

there was no dealer nearby where we were and it was Memorial Day weekend. That is an interesting link. May try an old BMW radio on it just to see how correct it is!

 

[mechtech2]

If the battery V drops to 12.2 overnight, it is no good, or there is a big parasitic draw.
Pull fuses to check which circuit the draw is on, while an ammeter to ground is installed.

 

[wrcsixeight]

I've put my 2/12/25 amp charger on many questionable batteries.

When I see the voltage rise very quickly on the 2 or 12 amp setting, I know the charger is either going to turn itself off shortly, or just go into float mode, doing little charging.

Desulfators are not some magical battery restorer. Many would argue that such a feature is a worthless marketing scam. A controlled overcharge monitoring temperature (less than 120 f)with voltages in the low 16's will likely return more lead sulfate to the electrolyte and restore a portion of capacity much better than a magical pulse desulfator will. Finding a charger which will go up into the 16's is the bigger challenge. Unhook the Automobile's leads before charging a battery up to these high voltages if you leave it in vehicle, and don't try it on an AGM battery.


A 5$ hydrometer can tell you a lot on a flooded, non maintenance free battery. The Glass ones give more consistent readings IME.


An aging battery is like a Gas tank which keeps getting smaller.

You can still fill it up, but it does not take very much to charge or discharge what is left.

 

[JHZR2]

Originally Posted By: mechtech2
If the battery V drops to 12.2 overnight, it is no good, or there is a big parasitic draw.
Pull fuses to check which circuit the draw is on, while an ammeter to ground is installed.


I would have pulled the battery but didnt want to loose the radio code. Will explore more next time I am near the car. It is one of multiple, so there isnt a huge rush.

I did verify the battery is from Feb 05, so it may be near its usable life anyway...

 

[mechtech2]

You can hook up a 9V battery or a charger to keep your radio and clock settings [also the fuel trim in the computer].