I got an original 7 year old batt in my Civic. Last time I got an oil change they ran a test on it and it was in the orange. IE needs to be replaced soon.

Car start fine first crank in the cold weather, AC works fine, Radio with AMP doesnt fade out.

What I did notice and its very lightly and hard to tell, is when the car is idling the headlights get a little dimmer. I havnt noticed this before, seems to do it in below freezing.

Would that be the aging battery or the alternator?

 

Cold weather will definitely mess with a battery's ability to operate at its fullest. However, this situation is likely an alternator thing - it should be picking up the slack of the battery. If it bugs you, you could replace the battery and see if it goes away. But, since it's not having any cranking issues whatsoever other than a little light dim, it could just be the alternator not putting out much power at idle, perfectly normal for a stock one.

 

Does this happen even if you have all the other accessories off? My battery has been in use for 6 yrs and I do not notice my headlights dimming when the car is at idle.

I don't think dimming should happen at idle because the 7th gen civic has an electrical load detector circuit which bumps up the RPM (only a tiny bit) when any of the accessories need to draw more current from the alternator. The engine RPM will usually shoot up before the electrical load bogs down the engine.

On older hondas w/out the ELD, it's very noticeable when an electrical load turns on because the engine rpms will drop momentarily before shooting back up. With the ELD, it's harder to notice this. I notice it just a tiny bit if my hazard lights are on, I can hear the engine repeatedly bump up the RPM then let it back down as the flashers go on and off.

Since your battery is already weak, go change it. The dimming problem might go away.

 

i think if his battery likes to self-discharge when the car is off, the alternator will spend more time putting out near max current just to charge the battery. the alternator won't have much current output capability left for accessories.

btw even if a battery self-discharges rapidly, there's usually enough reserve capacity left to start the car if the car is used every day. lead acid batteries have very low internal resistance. they will often still turn an engine even if the capacity is near empty.

 

This happens without any additional loads other than the radio. I do have after market pulleys but that's it. I haven't notice it happening yet and don't see this as a problem. Just wondering what the cause is.

 

the aftermarket pulleys are most likely to have caused the problem...

btw, the stock radio isn't exactly a big load..stuff like the rear defroster, headlights, fans etc draw more current than the stock radio

 

its not stock, i have a small 200 watt amp

 

i already said it's your pulley!

those are designed to lessen the load on your engine...it does that by taking power away from the accessory stuff such as your alternator. if your alternator isn't spinning fast enough anymore, it won't output enough current.