Alternator or battery?

[TDot]

The past couple months, once in a while when I pull up to the lights and I'm sitting there for about a minute and a half, the power will cut in and out totally once....(the car wont actually stop though), or hint that its about to do it. I dont have the system blasting, or near obnoxiously loud, but simply "enjoyable". Is that a simple indicator on if it's the battery or alternator? I have a voltage indicator that I can watch from in the car, and I can see my battery voltage dropping to average 9-11v and averaging 12 while stopped with the music playing (decent bass). I know that may seem obvious..."well its your battery", but I thought once the car/alternator is running, it's supposed to keep your battery up. So, which is going bad?

[kmiles]

I've had a similar problem before and it can actually be either one. I think the only way is to take it somewhere they can test it. I have an interstate battery store near my office and over the years they have been great - it it wasn't the battery, they didn't try to sell me one.

One other thing you might look at - is your belt slipping? I recently changed out my belts and my Alt belt was slipping and I saw some erratic electrical problems that went away when I tightened the belt to spec.

[szh]

Could be either ... but if the car is running, I would be more suspicious of the alternator. It should provide enough current when running well to not get overwhelmed by a stereo system at volume, I would think.

Yeah, 9 to 11 volts is way too low for a battery under normal conditions, but that measurement is with lots of current being drawn - the voltage can drop quite a bit at that point.

Z

[BlackCat81]

I assume you're talking about an aftermarket stereo system? If so, do you have a capacitor installed?

[TDot]

I put new belts on back in September I think, and it was good and snug. I'll double check them to make sure, but I think they are good.

Im going to run some tests on the alternator and battery with and without load and see where everything stands. I'm nearing 100K so maybe my system taxed my alternator since it wasnt designed to output the required amps? Does anyone know our alternator amp output?

No capacitor. Those are a waste and potential bottleneck. I would be better off putting in a backup battery with better reserves than a capacitor. Capacitors would be better suited for dynamic music with longer quiet passages if anything.

As a side note...I may start a second thread for this because I dont know if it's directly related or something else going bad...this has happened twice now in the past 10 days. I came out in the morning, opened the car with no problem, sat down, closed the door, pushed the button, NO POWER. i put the fob in the slot and nothing. No dash light, no alarm light, nothing. I get out the car push the button on the door, it locks. I unlock it, get in, push start, and everything comes to life. I checked the battery and the contacts are nice and tight and clean. Related or seporate thread?

[cruzad3r]

when my battery died, i had the same symptom. the door would open but the car wouldn't start. best to have your battery tested.

[steve_c]

Well,
No one asked so I will.

How old is your battery?

You really are chasing your tail doing any checks without first verifying your battery is up to snuff.
Have the battery cells been checked to see if any are going dry?
In order to do a proper battery testing, you need to fully charge the battery before applying a load test on it.

Yes, the no power up issue is most likely related. Most vehicle electronic components will not power up if voltage falls below 10v.
You can check to see if this could potentially be the issue....

Let the vehicle rest overnight, In the AM put a voltmeter across the battery terminals and read the battery base voltage. (do not start car or turn on ignition).
It should be above 12.4V, (12.6V is the optimum ideal reading).
What do you get?

I see you are in NY (as I am). You can get 5 to 6 years out of a battery easily with no problems, but after that you are on borrowed time, (especially in your case, as your audio may be adding a significant load to your system).

[Ilya]

My battery died today while I was in the Sears parking lot (caught a small nail in my tire). Original Infiniti battery (I'm assuming)...so 5 years old or maybe even 6, 72kmi. Got the new one in right on the spot (Sears guys were nice enough to loan me a 10mm wrench and a flathead screwdriver)...car seems to do everything better. Bass is thumpier, tweeters cleaner, starts better obviously, etc.

If the battery is around the same age as mine...just go ahead and change it. It's time.

[TDot]

As of right now it looks like it was the battery connector. The posiive termintal seemed tight when wiggling it, but when i focused on it a little more and decide to try and twist it, it did so with relatively little effort. I unhooked the clamps, reshaped it best i could to cover the entire terminal (still not the way i would like it), and tightened it down. I havent had another incident so far. My indicators inside show higher voltages as well. If things continue like this for another two weeks Ill call it fixed.

[szh]

Ah! Good to know.

I would also recommend using a battery post brush. These fit over the terminals - as you rotate them, the wire in the brushes really shine up the metal on the terminal posts, removing any oxidation or other gunk for a solid electrical connection.

Z

[The00Dustin]

Sorry I didn't suggest that, I completely forgot about my similar experience a couple years ago. I'm pretty sure I posted about it when it happened, but your symptoms didn't trigger my memory, presumably because they were mostly different. My 2006 M45 acted like everything was fine until I hit the start button to crank the engine; it seemed like turning the starter was killing the battery (everything would die when it tried to crank the engine).