Generic Battery voltage/charging questions

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Generic Battery voltage/charging questions

Postby Oro » Sat Apr 11, 2020 7:13 pm

I understand battery basics reasonably well. I am trying to figure out how to handle a neighbor's newer Subaru that is not driven much.

I have an elderly neighbor with a really nice, 2016 Subaru Outback Limited, 12k miles on it. He is not driving it now so I am trying to tend it periodically for him. Up until mid-winter, I was driving it once a week but then I got busier with other things and let it set a bit. I wasn't worried. I drove it the other day, maybe a total of three different 15 minute segments (so only, say, .75h x 100amp charge into it, 75 amps). I checked it today and it was at 12.25V. The battery was replaced 12/18 under warranty with a dealer Subaru battery (unknown OE, but I imagine good). I have been worried because I wonder why it needed a new battery in 2 years. I have not done a leak-down test and I guess I should.

questions:

a) I think a car sitting at least several weeks, then driven 45 minutes that shows 12.25V (50/55%) is ok. 1.3 year old battery.

b) Battery voltage slowly trickled "up" as I measured it. I don't understand this. I put my multimeter across the posts and it read 12.1V, which upset me. I disconnected it, reconnected it, and it was 12.15V. As I held it on their, it slowly kept climbing - slowly, until it got up to 12.26V and I quit. Why is this?

I used to ask these kinds of questions at Bobistheoilguy, but it just became too loud and full of noisy know-nothings, I got tired of wading through the noise to get the few excellent answers.

Thanks!
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Re: Generic Battery voltage/charging questions

Postby Ed Mc. » Sat Apr 11, 2020 9:29 pm

Nominal charging voltage should be somewhere between 13.5V and 15.5V. Did you ever measure the battery voltage when the engine was running? If it's a bit on the low side, it should at least rise when you raise engine speed above idle.

After 45 minutes of driving/charging, unless the battery was really "flat" it should have brought it up higher than 12.25V.

What you could do is put it on a charger for a day or so then measure voltage. Measure voltage again with the engine idling then with a bit of throttle.

Or just take it to Autozone and have them do a free charging system check! Maybe the real reason why it needed a new battery so soon in the 1st place is a problem with the charging system.

I'd say the change of voltage when metering might be due to a capacitance effect. Or, if you're using an analog meter, it's affecting the internal resistance of the battery and that changes the voltage a bit. Probably just an anomaly.

Your neighbor might consider a charger/maintainer since he's not driving much. I've installed those on my Trooper, '67 Mustang, garden tractor, my Mom's 2 Mustangs and her F-250 (she can only drive one at a time! Then they sit a lot over the winter). They work very well and the ones I installed have a pigtail that permanently attaches to the battery, then you can easily plug in the charger, and quick-disconnect when you're ready to go. Just leave the pigtail hanging out a bit and then you don't have to open the hood to get at the connection.

This Black & Decker model is cheap, comes with the pigtail connection, and works great:

https://www.amazon.com/gp/product/B0051D3MP6

Hope that helps, let us know what you figure out............ed
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Re: Generic Battery voltage/charging questions

Postby Ed Mc. » Sat Apr 11, 2020 9:33 pm

In thinking about it, the pigtail wouldn't be long enough to hang out the front. What I recall doing is tie-wrapping the whole charger inside the engine compt, then running the 120VAC power cord out the lower front and securing it, so it's easy enough to reach that you can just unplug the extension cord when you go.

Works pretty well, that's how I set up the Trooper and her F-250 (and my 93-yr-old Uncle's Corolla, he doesn't drive much either!). Mom's Mustangs sit in the garage over winter, so they don't really need a cord hanging out front. Installed the pigtails instead and it's easy enough to pop the hood in the fall and unplug in the spring.
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Re: Generic Battery voltage/charging questions

Postby itsmehb » Sun Apr 12, 2020 9:29 am

I used one of those battery maintainers on my corvette, which I only drove on weekends for 10 years, and it worked great. But that probably isn't the answer your looking for.
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Re: Generic Battery voltage/charging questions

Postby DSUZU » Sun Apr 12, 2020 11:51 am

When sitting, parasitic drain on the battery will eventually draw it down. Parasitic drain would be the computer memory and any other systems that draw from the battery. Disconnecting a GOOD, but low charge battery from the vehicle SHOULD show a slight charge increase as the battery picks it's surface charge back up. This is the same principal if you have run a battery down trying to start a vehicle, and over night, it seems to have picked a charge back up.
If a battery gets REAL low (or dead) and you jump start and charge it by driving the vehicle, this is bad for a battery and will eventually kill it. The sudden high amperage charge on low or dead cells damages the cells. Some years back as we were outfitting our Police fleet with the new (then) radio systems, our communications shop left the keys on each car on all day while they did their work. Afterward, they jumped each vehicle and let them run to charge the batteries back up. Almost like clockwork, about a week later, each vehicle had a dead battery, usually while on shift and when shut off between calls. I happened to be on call during this time and made plenty of money replacing batteries before I convinced our upper management to put a stop to the key on nonsense. A trickle charger might be a good investment. Dennis
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Re: Generic Battery voltage/charging questions

Postby Oro » Sun Apr 12, 2020 2:14 pm

After 45 minutes of driving/charging, unless the battery was really "flat" it should have brought it up higher than 12.25V.


That's what I was looking for and am realizing now. 60 amps (let's say) should have brought it up more; I am referencing time-to-charge tables now.

I did verify the alt. is good, and in the past it was on a trickle charger (it broke this winter). I intentionally left it off the trickle because I wanted to find if it had a battery/charge/drain problem while it was still under extended warranty. I need to take it into the dealership anyway soon for a leaking rear tail-light assembly. I wanted to nail down the battery issue to make them deal with it at the same time.

I likely need to do a parasitic draw test. I have done them in the past on vehicles, including my trooper when it was draining down. I found the VR assembly in the alt was bad.

I am going to put it on a 10amp or so charger today while I'm out, take it off tonight and test it in the am tomorrow. If still low, then check the draw. If adequate/in spec, I'll let the dealership replace the battery again and start fresh.
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Re: Generic Battery voltage/charging questions

Postby Oro » Tue Apr 21, 2020 2:07 pm

To follow up, I wasn't happy with the result of driving so finally disconnected the ground strap to check the drain. It's drawing 660 to 700ma so...

It's a 2017 with an extended warranty; I'm taking it to the dealer this week to let them wrestle with it - but this time I know so they can't do to him what they did before and just slap a new battery in and call it good. ;)
1998 Acura SLX. OME 929s and front crank, KYB tubes. Retro'd Aisin manual front hubs.
Home rebuilt 4L30E doing great. Aux cooler and temp gauge. Big thanks on the rebuild to Buster28, Jerry (jlemond), CalG, and others.
Factory(US dealer) side steps and roof/ski rack (Yakima).
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Re: Generic Battery voltage/charging questions

Postby Ed Mc. » Tue Apr 21, 2020 3:24 pm

All the electronics on newer rigs will have a parasitic draw, but that seems excessive. Could be the root cause of the problem. You'd have to have a trickle charger of 1 amp or more just to counteract the current draw!
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Re: Generic Battery voltage/charging questions

Postby 93trooperpooper » Wed Apr 22, 2020 9:57 am

using the alt to charge a dead battery will also shorten the life of the alternator.
these new vehicles can have upwards of 20 + computers, and all of them draw a little power. most newer vehicles have it set up so that if the battery drops below a set voltage, the main ecm will ''turn off'' the battery, leaving just the anti-theft working....until the battery is completly dead.
will drive these until they quit and move onto something else.
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Re: Generic Battery voltage/charging questions

Postby QuantumRift » Thu May 14, 2020 11:55 pm

Even 'new' batteries can fail. Case in point: I have a 2004 GMC Envoy 5.3L XUV. Only 85K miles. Installed a new DuraLast Gold from AutoZone about 18 months ago. Last week it went dead. Charged it up, and in two days it was dead again. Charged it again (slow charge), and in two days it was dead. Got it running, checked the alternator, which tested good. Took it back to AutoZone and got another new DuraLast Gold. Batteries fail. They're not all made like they used to be made.

Rule of thumb: Buy the cheapest battery that has the CCA you need with the LONGEST warranty. Never go wrong there.

As for tools, invest a few dollars in a battery load tester...it will return your investment in GOLD in no time. Plus you can help all your friends. I have a DieHard digital battery charger with alternator charger but it often can give an erroneous reading on a battery, so I also have two older ANALOG battery chargers...you know, the kind that won't 'shut down and stop charging and read badbatt'....I've saved more batteries using analog chargers over the years.
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Re: Generic Battery voltage/charging questions

Postby 93trooperpooper » Fri May 15, 2020 9:06 am

QuantumRift wrote:Even 'new' batteries can fail. Case in point: I have a 2004 GMC Envoy 5.3L XUV. Only 85K miles. Installed a new DuraLast Gold from AutoZone about 18 months ago. Last week it went dead. Charged it up, and in two days it was dead again. Charged it again (slow charge), and in two days it was dead. Got it running, checked the alternator, which tested good. Took it back to AutoZone and got another new DuraLast Gold. Batteries fail. They're not all made like they used to be made.

Rule of thumb: Buy the cheapest battery that has the CCA you need with the LONGEST warranty. Never go wrong there.

As for tools, invest a few dollars in a battery load tester...it will return your investment in GOLD in no time. Plus you can help all your friends. I have a DieHard digital battery charger with alternator charger but it often can give an erroneous reading on a battery, so I also have two older ANALOG battery chargers...you know, the kind that won't 'shut down and stop charging and read badbatt'....I've saved more batteries using analog chargers over the years.

yup, i have seen the fancy digital chargers ''fail'' otherwise good batteries, and the same batteries came back to life with an analog charger- hot charge for a few minutes, then a 2 amp charge overnight. usually they come back.
i have a 500 amp carbon pile manual battery tester, as well as two smaller heating element style testers.
will drive these until they quit and move onto something else.
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Re: Generic Battery voltage/charging questions

Postby Oro » Thu May 21, 2020 1:33 pm

So the dealership had it for a day and a half and found nothing wrong - though they did re-flash a software update to the charging logic. Supposedly there had been an update since 2017 for it. We'll see happens.

As an aside, they gave me a 2019 Outback as a loaner since it's under extended warranty. Interesting to note how they had clearly improved some switchology on the wheel and center cluster. Some things I had found illogically placed were re-arranged and better. Clearly, they believe in running refinements.

Also of note what a dog the 4cyl (the loaner) is vs. the six in my friend's 3.6R loaded Outback. Very different driving experience, at all speeds - not just with the pedal down.
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