Battery Charging Question?? - JeepForum.com
 
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post #1 of 9 Old 03-19-2017, 02:56 PM Thread Starter
JackB1
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Battery Charging Question??

My 08 3.7 has not been getting a lot of driving lately. I checked the battery charge with my voltmeter and it registered 12.25 which is about 50%. The battery is only about 2 years old and everything works fine. I have a 6 amp charger which I hooked up. The needle immediately jumps to 5 amps but then in short order will drop back to about 1 amp. Is this normal?

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post #2 of 9 Old 03-20-2017, 12:51 AM
underscore
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Why is 12.25 50%? Is it having trouble starting?

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post #3 of 9 Old 03-20-2017, 08:06 AM
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Reading the battery voltage is not a good test of its condition. If its starting fine and no warning lights, its likely good. Your battery chargers operation sounds normal for a fully charged battery. You can take it to a parts store and ask them to do a battery load test if you want it tested properly.

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post #4 of 9 Old 03-20-2017, 09:35 AM
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About 12.40 volts is a fully charged battery, and when it sits for a while (maybe not a real long time either) it'll drop to about what yours is reading. The only good, reliable ways to check the battery condition these days is with a conductance tester (checks the battery's ability to produce current) and a load tester (puts a load on the battery for ~10 seconds), and these will pretty much verify if the battery is good or not. With the proper testers, these tests can both be done in about one minute. I conductance test mine about once a month, especially in the winter.....takes about 5 seconds once I have the tester out of its case.

Like said above, if you're not having any starting/charging problems or electronic gremlins, you're probably OK. If you don't have access to either of these testers, most auto parts places will check it for you.....at least the load test.

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post #5 of 9 Old 03-20-2017, 07:36 PM Thread Starter
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I appreciate the replies. The reason I tested in the first place is that several years [and a battery] ago I took the WK to Advance Auto and had a load test done. The guy said the battery tested fine EXCEPT it was low on charge. He surmised, after a conversation, that it was most likely from limited driving. I left the charger on overnight and got a volt reading of 12.45 which is 75%. [12.65 is 100% according to my research] There are a million YouTube videos about using a multimeter to check a car battery. Of course the one I just looked at got a reading of 12.29 and they said the battery was good. Anyway, you are correct in that I have never had an issue with this over the years. Just being a little anal I guess.
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post #6 of 9 Old 03-20-2017, 09:41 PM
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Voltage is a good initial check, but it only tells parts of the story. The battery I pulled out of my WK has 12V but can't output any sort of current. I can test LED pods with it, but it won't even pretend to try to crank an engine.

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post #7 of 9 Old 03-20-2017, 10:37 PM
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Quote:
Originally Posted by JackB1 View Post
I appreciate the replies. The reason I tested in the first place is that several years [and a battery] ago I took the WK to Advance Auto and had a load test done. The guy said the battery tested fine EXCEPT it was low on charge. He surmised, after a conversation, that it was most likely from limited driving. I left the charger on overnight and got a volt reading of 12.45 which is 75%. [12.65 is 100% according to my research] There are a million YouTube videos about using a multimeter to check a car battery. Of course the one I just looked at got a reading of 12.29 and they said the battery was good. Anyway, you are correct in that I have never had an issue with this over the years. Just being a little anal I guess.
Your battery voltage will vary with temperature as well, so if you're comparing last summer to this winter, you might consider that. Is there another symptom, besides the numbers on your meter that have you concerned?

What kind of voltmeter are you using that you're that confident in the accuracy (to be concerned over 0.2V)? I use fairly cheap ones, and they don't always agree within half a volt. Also, if the internal 9V battery on your meter is dying, your reading will be off. I would drop a $2 9V into the meter before I considered buying a car battery based on that meter.

I was wondering how accurate these meters claim to be, and I was surprised to find my cheap craftsman meters don't even publish an accuracy on the web (that I could find). I checked the $350 Fluke V87, and it claims an unimpressive +/-0.05%+1 Volts. That means at 12 volts, they're only telling you to expect to be within 1.006V. Now, I don't believe a $350 meter would be off by that much so I'm guessing they sand bag to keep complaints down or to avoid some calibration rules.

I'm no battery expert, but I put my crap meter on the battery when it's been overnight or longer, and I'm happy to see anything like 12.25, although the big AGM I have now seems to sit at 13 plus (again, crap meter means I'm really just comparing how it looks now to how it looks when the rig isn't screwing up). Then, I start the rig and expect it to jump to at least 13.5, maybe 14.5. Even if I turn the headlights on. Then, I shut lights and heater fans off and after a couple minutes of idling, I shut the rig off. Then I expect it to sit above 13 and very slowly drop, if at all while I'm watching.

Another good thing to do is to use a similar test on another vehicle that's working fine, and compare the results.

If you want to test the battery drain, you can use your multimeter to do that, and it should be well under 100mA if I'm recalling correctly, and I would think it would be under 30mA.

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post #8 of 9 Old 03-30-2017, 02:56 PM
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Quote:
Originally Posted by JackB1 View Post
My 08 3.7 has not been getting a lot of driving lately. I checked the battery charge with my voltmeter and it registered 12.25 which is about 50%. The battery is only about 2 years old and everything works fine. I have a 6 amp charger which I hooked up. The needle immediately jumps to 5 amps but then in short order will drop back to about 1 amp. Is this normal?
A dying battery will show decent voltage. Voltage is not the best indicator of battery condition, as 90grandoneer and others above have stated.

A multi-stage battery maintainer is one of the best investments you can make for your situation. BatteryTender is a good brand. Mine puts out 0.75 amps. Sears has one for $30 that puts out 2.0 amps. Your battery will last longer with these hooked up when your Heep is not in daily service.
Whatever you buy, make sure it is multi-stage and automatic. Should have at least 3 stages of bulk charge/finish charge built in. My batteries typically last 5-6 years under this regime.

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post #9 of 9 Old 03-30-2017, 06:18 PM Thread Starter
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I do have a Battery Tender but my case is not one of leaving the WK idle for extended periods but rather driving on a regular basis but for limited miles. Not enough to let the alternator do its job. I am not charging with my 6 amp charger every several weeks but more like months.
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