Hi. the Battery is 2yrs old and I have a brand new alternater. But within the last month or so. I noticed my battery /voltage gauge goes down as I'm driving. within 40mins I have a dead battery. battery checks out good. alternater checks out good too. Do any of yall have a clue why it does this? Its getting old having to charge the battery everynight just so I can get to work the next day.

 

Checks out good how? I mean there's no way that both battery and alternator could "check out good" if this is happening. Battery doesn't even need to have a charge once the car is running the alternator should supply to ignition system - but it's not and thus the battery drain - your plugs are firing off the battery! Have you had them both tested in the car and running?

 

Yeah, take the car to a large chain auto parts store, like advance auto. When checking the battery, you can't just check to see if it's 12v or not. They have load measuring equipment to tell how many CCA it's putting out. They usually also have a device to check your alternator.

 

i had this same problem on my 90 after a new battery new alt and starter ... it turned out that one of the diodes in my alternator was shorted and it was just draining the battery.. i figured this out by letting the car sit over night and in the morning when everything on the engine was cold just touch the alt and if its warm theres your problem. its drawing all the pwr. but if that isnt it good luck to you . all my stuff had check good as well and worked when the car was running but if it sat it just had a dead battery.

 

You left everything on in the car over night ? I didnt understand that because mine is having the same problem ive been buying the nicest batterys and within a week there dead. My trunkk maotor doesnt work eaither it doesnt fully suck down could that be drawing power somewhow?

 

Could be a few things. My car had the problem where the connector on the altenator would come loose whenever I would floor the car. Corrected that with a new connector.
Could also be a short in the system check out this thread https://www.thirdgen.org/forums/elec...eps-going.html

 

When you have the alternator tested, pay attention to how many amps its producing at idle and 2000RPM. Many of these auto parts store guys do not know how to interpret the output and if producing any amps, they simply proclaim it good.

If you have a multimeter, check the voltage of the battery of itself when the car is not running. Then start the car and check the operating voltage of the car when it is running and you will see if its producing enough voltage to recharge the battery.

irock88 has a point, make sure that connector is a good one and exciting the voltage regulator or you will never have a charged battery.

What brand of batteries are you all having problems with? In my experience, batteries typically last about 2-3 years before needing to be replaced.