Author Topic: Car Battery questions - is it dead?  (Read 17061 times)

MoonShadow

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Re: Car Battery questions - is it dead?
« Reply #50 on: July 28, 2015, 10:43:52 PM »
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After parking and plugging it back into the charger, I noticed the charge level was back down to 50%...! Is that normal? I looked at the voltage and it was showing up at 13.07v. Before driving it around while it was charging on 100%, I noticed the voltage was above 14v. I'm a bit worried at whether or not the battery will drain enough (to where the car can't start) if I were to take it into work tomorrow. Ugh, it's really hard waiting for it to finish charging because it's *so* close yet so much uncertainty... and the charging seems to take forever on it. I guess I'm in a better spot than I was a week ago though.

It's probably fine if you were just driving around for a few minutes.  Chargers have to have a higher voltage to push energy into the battery, so when the battery is pushing back at full charging voltage, about 14.5 volts, then the charger thinks it's "full".  But starting and idling the car, without getting up some engine speed to recharge the battery again, drains the battery pretty good at first.  The good news is that they are designed to work that way, with a well used and well cared for starting battery usually sitting overnight with 13.5 to 13.8 volts.  Most people would consider that well charged, but technically it's only about 85% charged.  Since an increasing charge becomes increasingly more difficult as the "back voltage" from the battery increases, a true full charge is something that only happens with a dedicated charger or a long road trip.

Just make sure that your alternator is actually putting out 14.5 volts when the engine is running, and that you don't have a ghost load on the battery while the car is off.

jeromedawg

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Re: Car Battery questions - is it dead?
« Reply #51 on: July 29, 2015, 09:38:38 AM »
.

After parking and plugging it back into the charger, I noticed the charge level was back down to 50%...! Is that normal? I looked at the voltage and it was showing up at 13.07v. Before driving it around while it was charging on 100%, I noticed the voltage was above 14v. I'm a bit worried at whether or not the battery will drain enough (to where the car can't start) if I were to take it into work tomorrow. Ugh, it's really hard waiting for it to finish charging because it's *so* close yet so much uncertainty... and the charging seems to take forever on it. I guess I'm in a better spot than I was a week ago though.

It's probably fine if you were just driving around for a few minutes.  Chargers have to have a higher voltage to push energy into the battery, so when the battery is pushing back at full charging voltage, about 14.5 volts, then the charger thinks it's "full".  But starting and idling the car, without getting up some engine speed to recharge the battery again, drains the battery pretty good at first.  The good news is that they are designed to work that way, with a well used and well cared for starting battery usually sitting overnight with 13.5 to 13.8 volts.  Most people would consider that well charged, but technically it's only about 85% charged.  Since an increasing charge becomes increasingly more difficult as the "back voltage" from the battery increases, a true full charge is something that only happens with a dedicated charger or a long road trip.

Just make sure that your alternator is actually putting out 14.5 volts when the engine is running, and that you don't have a ghost load on the battery while the car is off.

Thanks, this morning it was still blinking at 100% and floating above 14v on the charger. I don't think it should be taking *this* long to get up to full charge even on a full discharge (it's been 80-90+ hours on the charger now!) I did a quick test, unplugged the charger and measured the voltage after a few minutes. Voltage dropped down to 12.92v and seemed to be decreasing by .01v every 15-30 seconds. I'm wondering if it will drop all the way back down to virtually nothing if I let it sit the whole day. When it's not charging and is just sitting plugged in, it sounds like it should be reading a consistent 13.5-13.8v and not dropping in voltage like what I observed. Any ideas?

EDIT: hmm, reading around it sounds like 12.6v is the magic number. So maybe I outta unplug the charger tonight and let it sit for longer to see if it finally 'rests' around 12.6v. Then I'll know it's in good shape.
« Last Edit: July 29, 2015, 10:26:44 AM by jplee3 »

a1smith

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Re: Car Battery questions - is it dead?
« Reply #52 on: July 29, 2015, 10:11:35 PM »
Thanks, this morning it was still blinking at 100% and floating above 14v on the charger. I don't think it should be taking *this* long to get up to full charge even on a full discharge (it's been 80-90+ hours on the charger now!) I did a quick test, unplugged the charger and measured the voltage after a few minutes. Voltage dropped down to 12.92v and seemed to be decreasing by .01v every 15-30 seconds. I'm wondering if it will drop all the way back down to virtually nothing if I let it sit the whole day. When it's not charging and is just sitting plugged in, it sounds like it should be reading a consistent 13.5-13.8v and not dropping in voltage like what I observed. Any ideas?

EDIT: hmm, reading around it sounds like 12.6v is the magic number. So maybe I outta unplug the charger tonight and let it sit for longer to see if it finally 'rests' around 12.6v. Then I'll know it's in good shape.

Yes, 12.6V is a good fully charged OCV (open circuit voltage) for a 6 cell lead acid battery.  My guess is that the charge took so long because the charger stayed in the desulfation mode for so long; it needed to since the battery voltage was so low.

Just sitting on the charger with the charger maintaining a float voltage should give you a voltage in the mid 13V range.

A quick check I mentioned up thread is to turn on the lights in the car for about half a minute; this will remove the surface charge on the battery.  This should get you down around 12.6V, maybe a few tenths of a volt lower.

If the battery voltage is a lot lower in the morning after sitting overnight with no load and no float charger (say, 11.n volts) then you probably have a damaged battery.  The deep discharge probably created an internal short in the battery somewhere which is making it discharge quickly with no external load.

jeromedawg

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Re: Car Battery questions - is it dead?
« Reply #53 on: July 29, 2015, 10:20:44 PM »
Thanks, this morning it was still blinking at 100% and floating above 14v on the charger. I don't think it should be taking *this* long to get up to full charge even on a full discharge (it's been 80-90+ hours on the charger now!) I did a quick test, unplugged the charger and measured the voltage after a few minutes. Voltage dropped down to 12.92v and seemed to be decreasing by .01v every 15-30 seconds. I'm wondering if it will drop all the way back down to virtually nothing if I let it sit the whole day. When it's not charging and is just sitting plugged in, it sounds like it should be reading a consistent 13.5-13.8v and not dropping in voltage like what I observed. Any ideas?

EDIT: hmm, reading around it sounds like 12.6v is the magic number. So maybe I outta unplug the charger tonight and let it sit for longer to see if it finally 'rests' around 12.6v. Then I'll know it's in good shape.

Yes, 12.6V is a good fully charged OCV (open circuit voltage) for a 6 cell lead acid battery.  My guess is that the charge took so long because the charger stayed in the desulfation mode for so long; it needed to since the battery voltage was so low.

Just sitting on the charger with the charger maintaining a float voltage should give you a voltage in the mid 13V range.

A quick check I mentioned up thread is to turn on the lights in the car for about half a minute; this will remove the surface charge on the battery.  This should get you down around 12.6V, maybe a few tenths of a volt lower.

If the battery voltage is a lot lower in the morning after sitting overnight with no load and no float charger (say, 11.n volts) then you probably have a damaged battery.  The deep discharge probably created an internal short in the battery somewhere which is making it discharge quickly with no external load.

Thanks! When I got home the charger was *still* apparently charging (blinking) at 100%. The readout on the Voltmeter was still hovering at above 14v or so.

I unhooked it and let it sit for a while. Then went back out before you replied and actually did turn on the lights, radio, air, and let it all run for a couple minutes. I checked again and the voltage was more or less around 12.6v. Sounds like a waiting game now - I'm going to periodically check voltage throughout the night and tomorrow morning. Hopefully it's all good. I'll probably let the car sit in the garage for another day since I'm carpooling somewhere with my wife right after work. But that'll be a good opportunity to see where the voltage is, not having been charged, at the end of tomorrow. If it still looks good, I'll try driving it into work on Friday (will keep the jumpstarter in my trunk just in case though haha).

dragoncar

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Re: Car Battery questions - is it dead?
« Reply #54 on: July 30, 2015, 01:59:34 AM »


I unhooked it and let it sit for a while. Then went back out before you replied and actually did turn on the lights, radio, air, and let it all run for a couple minutes. I checked again and the voltage was more or less around 12.6v. Sounds like a waiting game now - I'm going to periodically check voltage throughout the night and tomorrow morning. Hopefully it's all good. I'll probably let the car sit in the garage for another day since I'm carpooling somewhere with my wife right after work. But that'll be a good opportunity to see where the voltage is, not having been charged, at the end of tomorrow. If it still looks good, I'll try driving it into work on Friday (will keep the jumpstarter in my trunk just in case though haha).

Wow, you're really dedicated to your battery baby.

jeromedawg

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Re: Car Battery questions - is it dead?
« Reply #55 on: July 30, 2015, 08:51:15 AM »


I unhooked it and let it sit for a while. Then went back out before you replied and actually did turn on the lights, radio, air, and let it all run for a couple minutes. I checked again and the voltage was more or less around 12.6v. Sounds like a waiting game now - I'm going to periodically check voltage throughout the night and tomorrow morning. Hopefully it's all good. I'll probably let the car sit in the garage for another day since I'm carpooling somewhere with my wife right after work. But that'll be a good opportunity to see where the voltage is, not having been charged, at the end of tomorrow. If it still looks good, I'll try driving it into work on Friday (will keep the jumpstarter in my trunk just in case though haha).

Wow, you're really dedicated to your battery baby.

LOL! We're expecting our [real] first later this month... so I think my nesting instincts are starting to kick in - wait, aren't mothers usually the ones nesting? I think my wife's ways are rubbing off on me a bit much :O

Really though, I think I was excited to get the charger and apply it right away... never done anything like this so it's kinda cool. And it may have very well saved me a trip to the auto store. Worth trouble? Maybe not for most, but a cool project for me since my car hasn't been working for the longest time and we've gotten used to it hahaha
« Last Edit: July 30, 2015, 08:54:42 AM by jplee3 »

jeromedawg

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Re: Car Battery questions - is it dead?
« Reply #56 on: July 31, 2015, 11:00:07 AM »
Well, left it sitting overnight and all day yesterday without being plugged in and the voltage was consistently reading out at around 12.6v! I drove it around a little last night and it was fine. And drove it into work this morning. Aside from some wind noise creep from not perfectly aligning the door when I reinstalled it from other work I was doing, the car was perfectly fine. Hopefully it starts up later when I go home! I'm also planning to drive it down to San Diego this weekend for a fishing trip... hopefully there are no issues. I'll have the jumpstarter in the back just in case haha.

Thanks all for the tips on this! Super helpful and fun learning experience!

mayanktanwar

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Re: Car Battery questions - is it dead?
« Reply #57 on: October 07, 2015, 05:04:31 AM »
Not need to worry about, you should need keep maintain battery like water level, connection points and more.