aireq

I have a '03 350z. A few months ago I was having problems with coming down to my car with a dead battery. I put it on a charger to ensure the battery was full. Yet a week or so later it was dead again.

I figured it was the battery because as far as I knew it was the battery that came with the car (~6 years old). So I got a new battery and installed it in the car. Yet I'm still having the same issues. Lately I've fully charged the battery on a charger, and then after a week or so of sitting in the garage the battery is dead again. I don't use this car that much, but still the battery should not die after a week.

So my guess is something is drawing current even when the car is off and draining the battery. The car does have an aftermarket alarm that was installed when I bought it that I'm a little suspicious of. However, I'd rather not just disconnect the alarm and wait two weeks to see if it worked.

I have a pretty decent multimeter. Is there a more systematic way i can go about determining if and what is drawing current and draining the battery?

DavesZ#3

iTrader: (26)

You probably already guessed right - it's the aftermarket alarm.

What you need to measure is how much current is being drawn from the battery when the car is sitting.

It's not un-common to see people report that their battery is dead after sitting for two weeks or so. Your alarm may be worse than normal and draining it down after just one week.

Z PHAT Z

iTrader: (46)

If you have a Harbor Freight around you, then buy a battery tender for like $20. It will keep your battery charged at all time. It comes very handy if you don't use your car much. It also can revived dead battery.

aireq

I have a battery tender for my motorcycle. Would that work?


I read the article on this site, and here's what I found.


My battery has been on a 2A trickle charger for the past week or so. The voltage of the battery (with nothing connected) measured 13.18V.

The resistance across the alarm power cables measured 12.69 kOhm and seemed to hold steady at that point.

The resistance across the battery cables (no alarm) started at 165 kOhm, but continued to drop consistently. After 10 min or so it got down to 32.3 kOhm, but was slowly continuing to drop. Seemed like it was slowing down exponentially. My guess is a capacitor was charging.


Next I measured the actual current draw from the battery without the alarm connected. At first it drew ~0.5 A, but quickly dropped and held steady at 0.08A. With the alarm connected it held steady at 0.09A.

The article I mentioned above said the current draw shouldn't be more then .035A, which my car is above with or without the alarm connected. Still the current doesn't seem that much higher then the recommended amount.

What does everyone think? Should I start pulling fuses to see where the current is going?

winchman

If it was a capacitor charging, the resistance reading would get higher over time. Less current would be flowing through the meter as the capacitor is charged.

Of course, you might have had the meter connected so the battery in the meter was opposite to the car battery connections. If that's the case, the capacitor would be discharging into the meter when you first hooked it up, causing a high initial reading that gets lower over time.

Any kind of 12V battery tender would be able to keep up with that low a current draw. The question is how much inconvenience you want to put up with.

I'd find out where the current is going. If it's easy to get it lower, do it. If not, use the tender.

aireq

Yeah this is probably the case. I wasn't paying attention to which wire was connected to which.




I'd rather not have to put the battery tender on it. So I guess I'll start pulling fuses. However, is the current I'm currently reading considered high?

What is normal amount of current I should expect in a 350Z

winchman

A typical 350Z battery will have about 40 amp-hours capacity. That would last about 440 hours with a 0.09A load. After a week and a half or so, it would probably be iffy on starting the car. Getting the load down to 0.035A would more than double those times.

aireq

Ah yeah good point. Well at least the numbers are making sense. Time to start pulling fuses.

aireq

Alright now I'm really confused. Last weekend when my car was dead I put it on my charger,which has a 6A mode and a 2A trickle charger mode. I put in on the 6A mode. A day or so later I switched it to the trickle charge to keep it charged until I had time this weekend to deal with it.

So today I went and took it off the charger, and disconnected the battery to do all the tests I mentioned above. Last time I left it today I left the battery disconnected.

Later tonight my GF calls saying she needs to be picked up. So I go downstairs and reconnected the battery. Yet when I turn the key on the battery gauge on the dash only goes up to about 10V. When I try to start it the solenoid clicks rapidly, but the started does not turn over at all.

Again aside for the tests I did today after I took my battery off the trickle charger the battery has been disconnected all day.

So I put it back on the charger (6A mode) and the meter on the charger read pretty low like the battery was not charged at all.

Anyone have any idea why my battery was not charged?

OkashiZ

iTrader: (11)

its a dead battery if you charge it and it does not charge. once a battery loses all of the charge it will not regain energy.

aireq

Thanks for all the help everyone.

I took the battery back to the Kragen I bought it from and they found that it indeed had a dead cell. I got a replacement battery under warranty.