Battery Drain issue
 

Alright, before I start i'll say this, I searched and searched for literally hours, and did find some very useful stuff, however most things I found lacked specific instruction, and the persons w/ the problem would never post their results to conclude whether or not what they did helped.

I bought a '87 n/a Rx-7 last month. The guy I bought it from I know well & work with. He told me right from the start, that if you don't disconnect the battery and let the car sit for a week or so, the battery will drain to nothing. Boy was he right. The battery in it was a deep cycle marine battery, but he said he's charged it probably ten times so far....so i assumed the battery is probably smoked from too much re-charging at this point, although he did drive it 30 miles to my house w/ no issues w/ that battery in it. After getting the car, i park it, make sure everything is off, then lock it up. (battery still connected)

The next day, I tried to start it and got nothing, wouldn't even crank over. So i get out the jumper pack and it fires right up. I let it run for 10 minutes w/ the pack on it ( inside voltmeter reading 14). Then I took off the jumper pack and let it run more. Over the course of letting the car run for 45 min w/ out the jumper pack, the inside voltmeter gradually dropped down to 12. During all of this the headlights were on as well as the dome light(i was changing shifter bushing & needed light). Soon after seeing that the inside voltmeter was slowly dropping, I turned the car all the way off. Less than 5 minutes later i tried to start the car and NO DICE, it wouldn't crank. So now I have a brand new battery in it, but unhooked at the moment.

For about 20 min, i got my hands on a digi multi-meter, but was unsure of how to go about testing & where to test. It started to snow real hard so i didn't have much time. The only thing I was able to test was, w/ all doors & hatch closed, all things turned off, I started pulling fuses in the engine bay and testing across both blades where the fuse would touch. For everything I got pretty much no voltage, EXCEPT for the BTN fuse, which was reading 12.73 volts. Does this mean anything ? From what I understand, the BTN will have some draw on it, but 12.7 volts ?......

Any light that could be shed on this situation would be GREATLY appreciated. For the moment I bought a battery kill-switch, but thats like putting a band-aid on a amputated leg. If someone could tell me how to go about diagnosing this problem PROPERLY & w/ specifics w/ a Multi-Meter, that'd be awesome. Also, the alternator in the car is 13 or 14 years old, hasn't seen lots of mileage, but is AT LEAST 14 years old. Diode issue maybe ? Like i said, some help from the rx-7 electrical gods would be of great value right now. Icemark.....where are you at brother ? lol

Sounds like a few things wrong here.

When your car is running you say the volt meter slowly drops to 12v. Right? Better have your alternator checked. Your volts should always stay above 13v even if the battery is no good.

Is the alternator stock or is the alternator of a different year like an FD in a FC or S5 in a S4?.

You don't check volts when you want to see how much draw something has. Look at your multimeter and there should be 3 ports. 2 for volt/ohm readings and then an extra black port that will usually say 10A Max or something like that. Connect the black lead to that port and move the dial to that 10A port mark(not knowing how your multimeter works or looks like)

Then disconnect the main positive cable from the battery while the engine is off. Connect the red lead to the + battery post and connect the black lead to the main cable.

What this is doing is if there is ANY draw, the draw will be traveling through the multimeter and will be measured. You should have .00amps. I actually think there is a limit like .05amps or somthing like that.

You can also do this to the fuse block like you were doing and measure the amp draw. Volts mean nothing when it comes to finding out how much draw there is.

Since your volts go to 12 and continue to drop, im going to say your alternator might but pulling the juice. Since the battery has been drained so many times. Its dead. Buy another one and get that alt tested.

If the car is running fine once jumped...the alternator should be working I believe. I know when my alt died...the car ran until the battery ran out of juice...then the car died.

It's still probably a good idea to get the alt checked out tho because it could be doing just enough to run the car, but not enough to charge the battery and run the car.

Just carry it to autozone or advance auto parts...they'll check it for free.

Alternator test (thanks to Sureshot)
Engine running, headlights & heater fan on high:
Alternator post to alternator frame = 13.4-14.5 volts (verifies the alternator output)
alternator post to battery (+) = 0 volts (verifies the primary + wire)
alternator frame to battery (-) = 0 volts (verifies the primary ground)
Turn off the motor, but leave the lights on.
Battery (+) to battery (-) = ~12.5 volts and holds steady. (verifies battery)

It's a stock s4 alternator, and i know it's at least 14 years old. thanks for the help, i'll try a few more things....i have a new battery in it right now unhooked, and i'll get the alternator tested, i just don't have much faith in the Advanced Auto people to test things right, no offense but they are sometimes on comission and will just sell you crap for their own benefit.

Thats an ok test but that may pass with flying colors and still the alt may be bad.

The engine can run for a while without an alternator. Counting in minutes. I think untill about 10v or somthing like that depending on the condition of the battery.

True it's a quick and dirty test, but still pretty accurate. If you really want to be accurate, go with what the FSM says.

my car ran for like 35-45 minutes w/ the shitty battery, during that time, my volts dropped about 2.5, after that i just turned it off and 5 min later it wouldn't start, or even wanna turn over. hmm

2.5v eh? yikes. I personally thought it woul dhave died around 10. You sure it was 2.5v? I can't see much running after 9v.

So how is the testing coming? Find anything out yet?

He means it dropped 2.5 V from what it was at startup, not it dropped to 2.5 v.

You actually can do it by using volts, I just did it last week; voltmeter in series on the negative side. I wasn't concerned with how much amp it was drawing since I knew there was an issue; I just wanted to find the issue.

I will start by removing all NON OEM electrical connections (e-fan, aftermarket alarm, sound system, etc); and then start with the test.

You don't really need the a good alternator in order to find the leak, fully charge your battery, disconnect your alternator, and go to town with your voltmeter.

Sounds like what mine was doing. Check your grounds, if the battery is old and worn out, just get yourself a new one. Never hurts. If you have an alarm system, check to make sure its not malfunctioning. I had no horns and when mine would go off I wouldnt know it. It was slowely draining my battery. After I did all of the above it worked tip top

Bad or mis-wired alt and there may be current draw from mis-wired accessories.

But you have to fix the first thing before you can fix the rest

Stock alt.

ah ya. haha misread his post.

knowing how many amps are being pulled will tell you how large of a leak you have.

do a quick search on the net and you will see that you want to measure amp current. You shouldn't even put a voltmeter in series. Trust me.

Ammeters get connected in series
Volt meteres get connected in parallel.

Voltmeters are very high in resistance so they don't suck up a lot of power when testing voltages. Using them in series could give you the wrong reading or even burn out your voltmeter as they have very little circuitry.

Ammeters are very low in resistance so they don't alter the amount of current flowing through, or atleast any substansial amount. They are usually part of a multimeter and are usually fused at 10amps. They can handle a bit more for little time.

http://www.mightyautoparts.com/pdf/articles/tt63.pdf
http://www.doctronics.co.uk/meter.htm

ok, I had a nasty battery drain on another car. I did a simple test, basically with the engine off you disconnect the negative car battery cable and hook up either a test light or ammeter between the neg. cable and the neg. battery post. the amperage should be very small less than say 35mA or the test light should not light up.

If this is not the case and the test light is glowing or you have more than say 50mA than you have a drain and you should start pulling fuses until you find the problem. In my case it was the alternator. It had grounded itself internally.

And that will tell you what exactly? How is that going to help you?

Sorry, being there done that; I just found the issue on my FC last saturday :)

I am not saying that he shoulddn't do amps, what I am saying is that he can also do volts in series. Seriously, if you haven't done it; don't say that he shouldn't ;)

I guess that using a 12v tester light is out of the question for you?

That is kinda the idiot light way to check.

All that does is tell you that the test light works.

Only a multi-meter (as cheap as $20 at radio shack or home depot) will actually tell you if there is a draw.

and just for your info.. the stock FC electrical system can draw up to 45mA and be perfectly fine... so again your test would be useless. It is larger draws like 65+mA that you have to worry about.

Im not saying it will not work, im simply saying that you could burn out your volt meter or get a bad reading or modify the current flow through the meter since its resistance is high. Read up buddy. Just because it works for you doesn't mean you should go blurt out to everyone that it will work for others.

This is a little different. We are talking about a .99 cent item not $30+. Also I hope you are not talking about those battery alternator test lamps are you? If so, you are not using them right once again. Also you will not know exactly how many amps are being drawn. So YES, the test light is NOT going to work for me nor ANYONE else that wants to find out how much of a current (amps) drain there is.

Im simply telling you facts. Im not going to risk any of my multimeters to your suggestion of hooking a volt meter in series. Go search on the net, every where you go you will see that you should not hook a voltmeter in SERIES!

Amps have a much larger effect on the electrical system. Volts of a very little effect. You can run 1v and over 50,000v through a phone wire. Try running over 5-10 amps through that same wire.

Before posting something else. Go do some research.

ok guys, i borrowed a radio shack MM, has lots of settings so i'm sure it'll work. i'm gonna try a few different tests and post the corresponding results. thanks for the tips

it dropped by 2.5 volts, not to 2.5 volts.

99 cent tester light, HA!

I asked before, and will ask you again, knowing the EXACT amp drain, what will it DO for you?

If there is normal static draw of 50ma; and you test shows 75ma, what does that tells you? Would you start troubleshootin in a different maner that if the reading showed 90ma?

If you are using 99 cent voltimeter, I find it hard to believe that you have a DESCENT voltimeter :D