battery or alternator?

[apzak]

how do you know if you need a new battery or alternator? My mechanic said I need a new alternator, he checked the electrical system (told me to turn on everything, ac/defrost/wipers/lights/hazzards/everything) he got 13 volts and said it should be 14 volts. My battery is also old. Could the battery be the problem? Sometimes my lights dim when I'm using the wipers/radio/lights/fogs/ac/heat and if I turn something off (like the fogs) everything goes back to normal. So if there is a lot of strain on my electrical system it can't handle it basically. Is there anyway this could be a battery? (i'm hoping its the battery because alternator is $270 and I can imagine its a ***** to replace) Car has 80,000 miles, battery is interstate and atleast 4 yrs old, if interstate batteries are OEM then its most likely the OEM battery which means its 8-9 yrs old.. I really think the battery is 8-9 yrs, but I didnt own the car when new, I've had it for close to 4 years so I know its atleast 4 yrs old because I never replaced it.

There is a alot of blueish white chalky dust on the battery terminals whatever that means. Does the engine on an S14 need to be pulled out to replace the alternator? My friend needed to pull the 1.6 out to replace the alternator on a 200sx

[wayfastwhitey]

i'll leave it to someone else to tell you whether they think its your battery or your alt... but what i can tell you about the alternator is that the price should be closer to $200 (plus giving them your old alternator) depending upon where you buy it from....

i've changed mine a little while ago... wasnt too hard

engine definitely doesnt need to come out, little bit of juggling through the bay to drop it down after you unbolt it and a little wiggling to get it back in..... if it gets really tough i think you can remove the bottom of the fan and maybe a radiator hose or two... but i didnt do this

oh yea... having a friend will help, one above and one below makes the wiggling quicker

sorry, long winded

[ILikeMy240sx]

I changed my battery about a year ago...

When I turn everything on I also get 13v on the voltmeter gauge and yes it should be around 14v but so far im not having any electrical problems so I dont see the need to replace the alternator if its doing what its supposed to w/o any probs.

Since my batt is new im assuming its the alternator.

I used to get 14~14.5V all the time but sometimes it does fall to 13~14V but nothing seems to be wrong

[hybrid_flyer]

clean the battery terminals first, that crap os corrosion. If you have high resistance on the terminals, it means the alternator has to work that much harder to charge the battery. The alternator is not hard to replace. It sounds like it might be the alternator though

[SHIFTrl240]

take your battery to the local autozone and have them test it

[ILikeMy240sx]

isnt testing the battery just measuring the voltage across the two terminals or is there something more to it than that?

[skylinedreams]

I beleive they also check the amperage of the battery cause you could have a battery that checks out fine with 12 volts but with out the current its useless.

[ILikeMy240sx]

Ok didnt think of that.. Duh

so current and voltage across two?

[skylinedreams]

something like that you cant have voltage with out current but you also need a certain amount of current to turn over your car and run so many accessories. you do measure buth from the same terminals.

[Kr0n1k]

Also, if you're alternator isn't functioning properly, it can kill your battery in the process, so a new battery may be a temporary fix, but you'll find out which it is if the new battery dies.

[Moto Man]

If you have or can borrow a battery charger, put your battery on the charger overnight then take it in to a shop and get it load tested. That is the only way to tell for sure if a battery is good or not.

The 13 volt reading could indicate a bad alternator or bad battery; you have to do more testing to tell where the problem is.

[Silvia2b]

yes you should listen to Moto Man. You do not have amperage. You have amperage draw on the battery when a load is applied. If your alternator was bad it may not keep the battery charged when driving. Requiring that you charge the battery externally each time you drive the vehicle. If you are getting a 13 volt reading when there is a load (all the accessories running), it may be a weak charging alternator, but it is still working. don't replace it prematurely. What symptoms did your mechanic diagnose to conclude that it was your alternator was the problem source?

[574-240sx]

Yes run all options first then check ground at first before you take your battery to be checked.

[Spongebob]

You can check your alternator at autozone or pepboys too.

[WeldingHank]

most stock alternators can't keep up with all the accesories in the car, so 13volts with EVERYTHING on is probably what would happen even with a brand new alternator.