Mechanics

BMW 325I BATTERY PROBLEM

1992 BMW 325i • 200,000 miles

It won't start. I was gone a month in the summer & when I came back it wouldn't start but before that time I had no problems what could be the issue I got it to start with a jump once since that time to get it into my garage but it wasn't a permanent fix. What could be the issue?
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Guest
October 27, 2012.



How long did it run? Because of all the computers' memory circuits drawing current from the battery, three weeks is about as long as you can expect the battery to hold a good enough charge to start the engine. Older batteries will last even less time. A simple jump-start might get the engine started but it's going to take a good 15 minutes for the acid in the battery to become conductive to where it will even begin to charge. If you put it on a charger with an amp meter, you'll see the gauge reading starts out real low, then comes up in 15 - 20 minutes. That's when it's really charging.

With older batteries always charge them at a very slow rate for about an hour. Your generator puts out three-phase output which is relatively steady. Home chargers put out single phase current which pulses on and off 120 times per second. That causes the plates in the battery to vibrate. As batteries age, the lead flakes off the plates and using a battery charger on "high" accelerates that flaking due to the vibration it causes.

It sounds like you don't have a problem other than needing to charge the battery. Be thankful you don't have a newer model BMW or Volkswagen. Disconnecting the battery or running it dead would require a tow to the dealer to have multiple computers unlocked, and a REAL expensive bill. They designed in a lot of ways to bleed money from unsuspecting owners after the sale.

Caradiodoc
Oct 27, 2012.