Alternator Problem, Please help.

[240marcuSX]

I keep killing batteries.

I have replaced my battery 3 times, and my alternator once, and i still keep killing batteries.

My friend is a Lexus technician and has tested for parasitic draw on the battery, there is none, He has tested for continuity between the battery and the alternator, and there is continuity, I have removed the alternator and had it tested where i bought it (autozone, rebuilt Nissan, duralast alt.) and it passed their test.

The car will run for about 1-2 weeks fine without dying on me, and then my battery will go dead and not be able to start the car without a jump.

What are some things that I could look for that could be causing this, I need to figure it out because i have some distant races coming up and need the reliability.

I have removed the wiring for the antenna, door ajar lights, aiv, among a few other things. When i say removed, i mean i have cut the wires to make them shorter and neater, to remove uneccesary harnesses. I have wrapped each wire separately with electrical tape to make sure they're not grounding out or touching each other, could this have anthing to do with the problem?

please help me, thanks for your time.

[steve s14]

get another test done somewhere else to make sure that it was done right.sounds like there is definately something wrong with the starting / charging system.i would guess that maybe the alternator is charging but sometimes cuts out, brushes sticking possibly. or the diodes in the rectifier of the alternator is bad.

[BimmerTech]

Sears now use a handheld (midtronics) battery/charging system tester. It's like $10 to have it done, but it's a pretty nice test. Another easy test is to just measure the charging voltage at the battery while the car is running. Should be close to or over 14v. If it's not, check the alternator output at the alternator. Check for bad grounds, a bad ground can cause poor charging and thus dead battery's. Just because a battery won't start the car doesn't mean its bad, just not charged. Anyway, hope you find your gremlin.~BimmerTech~

[240marcuSX]

What grounds should i be looking at? ones in the engine bay specfically?

we connected the multimeter to the battery and let it run, and as it got warmer the Voltage got lower. but he said that was normal. and then it did something really wierd. it dropped down to like 3v, and then 4 and then 5 and so on. and finally went back up to 13-14 range, and i havent had any problems with it since.

[BimmerTech]

Start checking grounds from the battery forward. Specificly the actual wire from the battery to where it grounds, these get corroded internally often, so might look ok, but really is all gunked up. Take a voltmeter set to DC volts. Attach the neg to a known good ground of the frame. Then touch the positive lead to where the ground cable attaches to the car, then to the negative connector, then the neg terminal of the battery. You should see 0 volts at all of these points, if you have voltage the point at which you touched is your culprit. I'm not sure what test your friend was doing to cause the voltage to drop to 3-6v.~BimmerTech~

[240marcuSX]

something else that ive noticed:

when driving around at night, my head lights will sometimes get dimmer and dimmer, and ill rev it up to like 4-5k for a few seconds, and theyll get brighter again and stay that way for a good while. Also, my cruise control was cutting itself off the other day until i revved it up also, and then it stayed on and didnt cut itself off anymore.

Does this information help narrow down some possibilities?

[jserrano]

There should be a battery SENSE wire feeding back to a plug on the alternator. Maybe that line is intermittently loosing connection.

[240marcuSX]

You know that makes alot of sense. Would the car run without that plug being plugged in?? While we were testing the voltage, my friend unplugged it and plugged it back in several times and it didnt seem to do anything.

[jserrano]

The battery sense wire is how the alternator regulator provides additional amperage to keep the battery charged up. Overcharging, undercharging, and electrolyte loss is what kills most batteries.

Running the car without that plug connected can send the alternator spiking high voltage and kill more than the battery.

[LonelyDrifter]

This may sound stupid, but check the actual connection for the battery terminal cables. I replaced a starter and an alternator (both of which were indeed in bad shape) when my problem was corrosion between the actual wire and the cheap Walmart connector (tightens with two nuts). My car would work for awhile, and then suddenly be dead, might start again for a few days, then be dead again. This might not be your problem, but I wish I had checked mine sooner...

[S13inBatnRuge]

i had the same problem its not always battery sometimes check inside the connectors