Bad Alternator or Bad Battery???
 

Did a search and only found one thread with this topic and it really didnt give an answer.
I recently bought a 1st Gen 7 and have been spending alot of time going through and upgrading everything, hence, i havent been driving my 8 as often. The first week i drove the 8 3 out of 7 days and just a couple days ago (after it setting for 2 days with no driving) i tried starting it and it went very slow and finally fired up. I took it out and drove it for about 20 minutes then parked it. Next morning I went down and it started to crank over but then slowly it died down to just a rapid clicking noise. I yanked the battery, took it to Autozone, let it charge on their tester for 45 mintues, and found out the battery was fine. Soooo, i then went back to the house, put the charged battery in and it started up (was not a strong start though, a bit sluggish). Im thinking now its the alternator. Any thoughts? The plugs are new and the coils are SHOULD be fine (changed like 9-10k miles ago). Car is an 04 with 55k miles. I have had it since 38k miles and havent changed the battery nor the alternator.

you can have the alternator checked but i would try to charge the battery over night first

I'd replace the battery before the alternator. It's almost time to replace it anyways it sounds like.

how to
 

Loosen the negative terminal on the battery.
Jump the car so it will run. (if it won't jump start its the battery)
While its running, kick off the negative terminal. (does not mess up your comp.)
If the car dies then the alternator is not working to keep the car running.
If the car keeps running, it was just your battery.

ALSO advanced auto with check your alternator for free!

Interesting approach.

The simplest way to test the alternator is to put a volmeter across the battery terminals while the car is running. If the alternator is good, you'll see somewhere between 13.5 and 14.5 volts. (Official low limit for the RX-8 is actually a bit lower than 13.5). If it's not, you'll see something less than 13.

For a little more thorough alternator testing, turn on the lights and as many accessories as you can think of. Voltage should still be up there.

Do-it-yourself battery testing is a bit trickier. Even pros with official battery testing gear can miss that. But if the alternator is good and the battery goes dead after sitting a few days, odds are you need a new battery.

Ken

Its your battery.

A full charge takes over night, but its time to replace it.

4 years is plenty for a battery in this car.

Our truck alternator was craping out and that worked perfectly to figure it out. It was coming up with some crazy low numbers. If it is the alternator, the battery light will probably come on when you drive it hard, so you can consider that.

ive had tons of alterator and batt probs - in my old mustang - i ended up with a 400$ 200 amp altenator and a optima yellowtop batt - the batt is used to start the car - the altenator is used to pwer the car and charge the batt when its running = volt meter is the best idea, autozone can test the batt and altenator, i had a bad batt in my rx8 when i bought it. i brought into auto zone, they saide it wouldnt hold a charge , got a new batt, boom , no more prob. thats the best thing to do.if it s the batt, after u charge it, everytime u start the car, it will get weaker, thats how i knew mine was bad, i charged it, then started the car over and over, it got weaker every time i started it. i knew for sure it was the batt. do that. sounds like a bad battery.easy fix.make sure u get a warranty. next time it hapens, who cares , batt is free anyway. i hope its not the altenator , i never changed one in the rx8, looks kinda like a pain in the asss , good luck.

just don't flood it with the bad battery

Everybody else has covered it... voltmeter is easiest. I'd change out a four year old battery regardless, especially in TX where you know we have massive swings in temps.

I guess, usually, the voltage regulator goes bad on the alternator. Have somebody rev the engine while reading the voltage, and you'll see it climb off ~12-13V to the ~13-14V.

And, yes, many of the autoparts stores will do a free test that will also measure the amperage output on the alternator.

Last thing it could be is a bad starter or a bad ground.

It was the battery. Just went and bought one from Autozone, stuck it in and fired right up without a hitch. Just through me for a lil loop when i hooked the old battery up to the tester and the tech told me it was fine.....no, it wasnt:) Thanks all for the replies.