Rep Power: 0

I've noticed a slight dimming in the headlights and cabin lights - not a constant dimming, but a flickering from high to low and back. At idle or at drive. Do i need to replace the battery, or the alternator? I need to tighten my belt a little bit because it was new and I've driven a bit, makes a squeal when the ac is on. Is it because of that? I'd really like to not replace the alternator that ***** expensive. Hasn't had trouble starting ever or anything like that.

 
Rep Power: 126

What car do you have?

 
Rep Power: 0

Suppose that would have been smart to mention. 02 civic EX

 
Rep Power: 367

have someone test:

1. battery (how old is it?)
2. alternator (after you tighten belt)

 
Rep Power: 512

the belt squeal and your dimming "issues" are likely not related, just coincidentally occurring

Is it just a slight dimming, but noticeable? Like, when you're under load, you have full brightness, but when you start coasting or at idle, it seems to dim? If so, that's somewhat normal behavior. That's the ELD doing its thing as a sort of fuel saver method. Hook up something to monitor battery voltage, and if you see something like 14-14.2V at full load and then down to 11.9-12.1V at idle/low load, then you're fine. If you're worried about components having issues, get them tested before replacing them. I know AutoZone does free testing on both batteries and alternators.

 
Rep Power: 99

You have to do some testing to know for sure, but my experience was...

Wisconsin winter. Noticed the headlights would dim every now and then while the car was running around November. Car had around 134K miles with the original alternator. I thought maybe it was because of the cold or a weak battery, but didn't think much of it since the car always started fine.

In February, the car just stalled on my way to work. It was a bad alternator.

What's the mileage? Is it the original alternator?