Ok before I start let me mention what parts are brand new and have been replaced:

Alternator
Starter
Alt Fuse
Belt that drives alternator

Also there is no parisitic or key off draws on the electrical system. Battery tests fine at walmart with their load test.

Here is the Problem: When I start the car and let it idle at operating tempature I clip my voltmeter to the battery terminals to read the charging output, the reading I get is (13.8v) when I put a load on (Radio,Lights,A/C) the voltage has dropped as low as (13.2v). I have heard people say that 13.5-14.5v is normal but in my automotive manual for my make and model says specs should be within the following range (14.1v-14.7v). So I took my friends battery out of his car and put it in mine, ran engine at idle and measured the voltage at (14.28v). So my question is, why is it that the alternators output changes when I put a different battery in? (battery fluid low? Faulty battery components?). I can't seem to find any articles that would tell me about this issue of mine.

Please advise me on what to do? fill batt with fluid, return for warranty, etc.

PS. when I try to return to walmart for replacement they run a load test and the batt passes then they say the battery is good and won't let me return it.

You didn't mention the age of your battery or your friends, nor the kind of car your friend has. It could be that your battery is just getting older. It could also be that you have some old, corroded, or poorly grounded battery cables. Or the alternator you have may be adequate but not as powerful as the OEM part. Check and clean all the connections and check your battery...if it's over 4 years old, it's probably ready to be replaced no matter what the warranty says.

Personally, I don't see the need to worry over half a volt or so since every car/battery/alternator combo will be different. 13.5 to 14.0 Volt range is good enough to maintain a battery's charge. 13.2 is a bit worrying...you are correct in that over 14 Volts would be ideal since this allows faster recharging. Lower outputs can allow the battery to slowly lose charge if the car is started constantly and driven for short trips or alot of accessories are used at once.

Why did you want to check the alternator output in the first place? Are you seeing symptoms of a week battery or alternator?

well my battery is about 2 years old, and I'm not sure how old my friends battery is. battery cables have been cleaned and have a very good contact.


The reason why I checked the voltage is because I was following my repair manual when I replaced the alternator, and it says to check the voltage and make sure its withing the 14.1-14.7 range. Another reason is just that I want to make sure my charging system is operating properly.

Also there was a sheet of paper included in the box saying how a bad battery or voltage regulator could kill the new alternator.

I suggest taking your car to an auto parts store that offers free testing of the entire charging system with the battery and alternator still in the car. Make a few phone calls to auto parts stores in your area and ask if they offer this free test. See if their testing system gives the same result as the one at Walmart. Some testing equipment can do more sophisticated tests than just putting a load test on a battery.

Mike

Two threads were merged.

I replaced the alternator under warranty.

Right after, I had walmart do a charging test and they gave me these results.
No Load: 13.74
Loaded: 13.61

A couple days later I had a mechanic check the charging system and it measured out at.
Loaded: >14v

So maybe my battery was low from the old alternator not charging properly and once the battery was fully charged it went back into spec. Since a full battery would put less of a strain on the alternator. Does that make sense?

Yes if Walmart didn't charge the battery as they should have before performing the load test. What a shocker!