Electrical trouble BMW Z3 2002 ?

Asked by Mar 21, 2010 at 03:30 PM about the 2002 BMW Z3 2.5i Convertible

Question type: Maintenance & Repair

Battery shows fully charged but won't start unless jumped. Now what?

4 Answers

2,145

Hi, It depends on what you mean by "fully charged". Does that means it has 14 volts when measured with engine running and does not drop below 12 volts under heavy load (with all consumables on)? Is it a newer battery or still the original?

1 of 1 people found this helpful.

Had it on BMW car charger for couple days. Original Battery shows 'green light'. Will start when she is jumped by another car, but will not start on her own when ignition key is turned. No other items (radio, lights) are turned on when trying to start the car. Don't have other battery tester that would show active volts when engine is running. Jumped her and took her over to someone who could test it thinking we needed new battery. They tested her and found batter was "fine". Next day, could not start car. Put on charger over night. Next morning started but at end of work day, had to have jump to get her home again.

2,145

Hi, the BMW trickle charger is not going to bring a flat battery back to its full charge - it is only intended for preventing a fully charged battery from discharging while the car is in storage (while the alarm systems, etc. continue to drain the battery). Our cars require all the juicy the battery can give to fire up and it sounded like your battery is not holding its charge. Once a battery (let alone an older one) is over discharged, its ability to become fully charged is permanently compromised and may need to be replaced. 6-8 years (less if the car sits a lot) is the average life of our batteries, a new factory or aftermarket replacement will be good for around 4 years due to regional environmental regulations placing limitations on the materials allowed to be utilized. I have used Interstate batteries in my bimmers with good results.

1 of 1 people found this helpful.

Thanks for your advice. We left it on the charger over night and will go try to start it up to see what happens. We had the feeling we were going to be up for a new battery all along, was just trying to hold off on it if we could find another method (aka cheaper) to fix our problem.

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