Question = low battery

[UDM Motorsport]

Ok i parked my car last thursday, undid the battery teminal, remove ecu, connect battery terminal back. Car sat. Yesterday, went to install ecu with new chip...undid battery terminal, plug ecu in and reconnect terminal. Tried to start and wont start...lights dim.
Took it to Autozone and they said battery low so they charged up and it held the charge.
Its a Optima Redtop - not sure how old...but looks fairly new.
Plug the recharged battery in today, car fired up right away.
When i shut the car down, on the dash the batt. light lites up and i'm turning the key off.

Is this normal or do i have some connection issues?

thanks
franklin

[nando]

if the light is on when the car is turned off, then you have a drain somewhere.

[mbonder]

if you turn the key to the ON position and the battery idiot light goes on then you have a problem with one of a few things. I am actually going through this myself at the very moment and waiting on parts.

Your battery is fine, that means that there is a drain somewhere, mine happened to be that starting the car was draining the battery because the alternator wasn't charging the battery while the car was running. So after a few starts there is no longer enough charge to spin the starter and you are left with a low battery.

To test this, look at the back of the alternator and remove the dust cover that is closest to the engine block(there are only two on there and this one is the smaller of the two). undo this wire and put your test light on it, if you have no power there then the brushes in the alternator as well as maybe the regulator are dead( this is what happened to me).

if you don't feel confident in doing this yourself, you could always take the whole alternator out and have it tested at a place like NAPA or the dealer.

There are obviously other things that could be draining this like a light that isn't turned off when you leave the car and whatnot, but if you eliminate those possibilities I would say this is a good one to try.

matt

[DaN]

The battery light on the dash is supposed to come on when the key is on, and the engine is off. The light should be off with the engine running.

[mikeedler]

and i know on the old E21s, if the light bulb is burned out in the dash, the car wont charge also..
If the car is running, the light should be out, if the key is in the on position and the car is not running, then it should be on. if you are turning the car off, the light will come on for a second as it is turning off. how cold is it where you are at right now. batteries loose a lot of power the colder the temp. is outside.

[UDM Motorsport]

It was in the 30s-40s all weekend long.

So i guess i'm ok then, since the dash battery light comes on when key is on and off when the car is running...comes back on when i turn it off for a second.

So could it be caused by the ECU not being in the car too?

I've left the car to sit for 1-2 weeks before and it fired right up...but it wasnt that cold either.

Thanks
Franklin

[DaN]

You most likely, left a door open or a dome light on, or the glove box open when you had the ecu out which drained the battery. It sounds like you have no problem.

[UDM Motorsport]

haha so much for a problem free car.

Well i plugged the battery in started the car drove for a bit...this was saturday morning.

Parked the car and tried today and no juice.

So obviouly i have a drain somewhere....anyone know where should i begin to look? or what are the common issues?

very unlikely the alternator could have caused this cause it was fine on saturday, sat for 2 days and no juice.

thanks
franklin

[DaN]

Check the bat voltage when its running to confirm the alternator is working, if yes then disconnect the negative bat cable and put either a test light or ammmeter in between the bat post and the cable. If it stays lit, there's a parasitic draw.

Then pull the fuses, one by one until the light goes out, or the amperage decreases.

[UDM Motorsport]

Ok i checked this issue today...the alternator charges fine.

When i shut the car off...the batt voltage drops to 12.85 just sitting there and every 4 seconds it drops by 0.01
Drops till 12.40 and it slows down....now about 30-60 seconds to drop 0.01.
I'm letting the car sit for about an hour now to see how much it drops.

What i did was remove the + cable and hook the multimeter to the loose + cable and the + battery terminal.

Under (mA) - it shows 0.29

I pull all the fuses one by one, and that number doesnt change.

anymore ideas on what i can do?


Or should i try it with the negative post now?

thanks
franklin

[Brew]

From the voltage dropping off like you're describing, it does sound like you have a key-off draw problem, but 0.29mA isn't all that bad if I'm remembering correctly.


Anything aftermarket on the car as far as electrical stuff? Stereo, alarm, etc... Those would be the most likely culprits.

Like someone said earlier, the best way to find out what is draining the battery is to have somebody pull fuses one-by-one while you watch the amperage on your multimeter. That will at least narrow down your search.


There's a chance that yo've got a bad battery too, and it just isn't holding a charge.

[Brew]

Or should i try it with the negative post now?

Amperage won't be any different because its the same circuit.