Hi everyone. I’ve been racking my brain on this problem for a few weeks now and I’m hoping someone on this forum knows where to steer me next.I have a 2012 Honda Civic LX with a little over 100k miles on it. A little while ago the car wouldn’t start. It sounded like a dying battery where the car would crank, but it wouldn’t turn over. The more you tried it the weaker the crank got before it just stopped altogether.

So I hooked it up to my battery charger overnight and went to start it in the morning. It turned over, but the cranking was slow and labored. Later in the day the car was “dead” again and I had to jump it. So I brought the presumed dying battery to the auto parts store and it tested as working with only a drop of less than 100 units (can’t remember what the units were called).I went back to the car and got some readings from my multimeter. At rest the battery was reading around 12.4V (not the usual 12.6V). Upon starting the car the meter jumped up to 13 or 14.xV, but then after a few seconds the reading would level back down to 12.4-12.5V. So I thought the alternator was losing its mojo. However, if I turned on the headlights, the multimeter reading would climb back up to 13-14.xV and back down once the lights were turned off. Strange? Maybe I have a smart car and it lowers the output when the battery is fully charged?

The next step was to check all fuses and also to do a parasitic drain test. This was all normal. I then had a realization that my cigarette lighter car charger had been acting up recently and wasn’t charging my phone. I rationalized that maybe this put too much load on the car and wore down the alternator and while the alternator hadn’t FAILED, it was failing. So I disconnected the car charger, charged up the battery and when I started the car back up the next day, it cranked and turned over like it was brand new. Yay, mystery solved! Nope. While all was hunky dory, over the next two days I noticed the cranking to get weaker each time until finally the car didn’t turn over again.This time I bit the bullet and went ahead and replaced the alternator with a new (remanufactured) one.

After the install I hooked up the multimeter and unfortunately had the same dropping voltage after a few seconds of startup (from 13-14.xV down to 12.4-12.5V). Poop. But I thought, hey maybe this car is smart remember? So the car started up normal for two days and then back to not turning over today. After I jumped it, I drove a 15 minute commute with my headlights on, thinking that increased voltage might keep the battery charge up like it's supposed to. So after parking and turning the car off I tried to restart the car and it turned over like a dream. So weird.

My next best guess is to replace the battery even though it tests okay (it is only 2.5 years old, still in three year warranty window) and/or test the starter. I don’t really think it could be the starter, nor do I want it to be the starter because it’s a pain to remove, but I’m running out of ideas and I’m tired of jumping my car. Also of note, when the car isn’t turning over, all other electronics work fine (door remote, radio, lights, etc). Yesterday while driving (with new alternator installed) I noticed my headlights were ever-so-slightly changing in intensity (almost slow-pulsating). Any ideas are much appreciated. Thanks for taking your time to read all of this.

TL;DR - car won't start. battery is good (tested) and replaced alternator. all other electronics work. starts right up with a jump; lasts a few days after a overnight charge, but cranking slowly decreases until no longer starts.

 

 

Thanks for helping Buc. I was actually thinking of just replacing the battery anyway since it's still under the warranty (and hopefully no charge to me). I'm planning on running it up to the store tomorrow and will update any progress here.

 

If the battery test good then the auto parts store will not replace the battery,
Why would they replace a good battery?

The charging system on Hondas are known as smart charging
If the battery is at a low state then the system should put out a higher charging voltage
And if there is no load then the ELD (electrical load detector) will tell the ECM to lower the output of the alternator.
Turning head lights on will put a load on the system and tell the ELD to tell the ECM to turn the alternator output higher.
This helps reduce the load on the engine and thus improve gas mileage
It also helps to reduce load on the starter motor when first starting the engine.
Note: the alternator has a connector with five wires/lines. Check to make sure there is no corrosion.

When an issue such as this comes up, the first thing to do is to check for parasitic drain.
Look up on youtube for more information on how to do this
If you believe that is not the problem then do as bucwheat says, clean all terminals and battery posts
Should also clean up grounds. Battery grounds, engine strap grounds.

Some people will do the big three upgrade to the electrical system when this shows up.
Big three ... 1. change the battery ground cable and terminals, 2. battery to alternator cable and terminals, 3. battery to starter cable and terminals

Note changing parts without actually knowing that they are causing the issue
That can become quite expensive and still not fix the issue.

 

Thanks for all the advice guys. I took the battery back to Walmart to try and get a new one since it was still in its warranty window. They said they had to test it and if it failed both of their tests I'd get another battery. The first test was with the handheld battery tester that gives you a print out. It showed readings a little lower than usual but not conclusive said the guy. So he hooked it up to another unit out on the shop floor and said it would take anywhere from 15 minutes to 90 minutes to test it and see if it takes and maintains a charge. After waiting for over 90 minutes <sigh> I got a new battery. Hooked it up and the car has been starting up like a champ. I checked to see if the voltage actually maintains the 13-14V range while running, but it did the same initial ramp up then back down to 12.5ish volts. So hopefully it's as you said @avisitor and my car has the "smart charging" system. Time will tell I suppose. I'll update again in a few days for the final verdict. Thanks again everyone.

 

Thanks for the update.
Hope the new battery is the right fix