My husband has replaced the battery in his 1990 BMW 325I, but the battery keeps dying on us. He says it isn't the alternator, because the car wouldn't turn over if it was. What else could it possible be?
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Re: Battery? Alternator? or what?
Hi and welcome to FixYa,
Initially, it could be the alternator or more specifically the voltage regulator inside the alternator. The function of the alternator is to produce the necessary charging voltage to replenish the charge of the battery. This voltage is then funneled and controlled by the regulator. Of course even if the alternator/regulator is good, there could be other possible reason(s) why the battery looses or is not charging such as loose wire/connector/terminals or a partial electrical short/fault draining the battery when parked.
To crank (turnover) the car's engine, a starter is used.
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Sounds like you have a dead battery. Try recharging the battery or get someone with jumper cables to give you a jump. If your battery dies again after driving for at least an hour you likely need a new battery. If the battery in the car is the original, it's time to replace it anyway.
renew the alternator ,its a bosch unit as original and the diode rectifier pack has a faulty diode ,change and get a bosch replacement unit and not a made in china cheapo their just juk and not worth the effort
If all your connections are clean and sound, then your car should be able to run without a battery. Start the car and disconnect the negative terminal. If it stops your alternator is faulty. This would explain dim lights that are draining the life out of the battery instead of being alternator driven. Same as the dieing while driving, the battery can't keep supplying power forever without being recharged by the alternator.
If the alternator is ok, the battery needs replacing. Repeated draining of batteries kills them.
Try to start again, then when the engine is start, remove the negative or positive battery cable, and if the engine die, the alternator is failed., and if not dying, alternator still good. But for me the way you said, I'm 100% your alternator is died. Need to replace a new one. And if you know how to solder, just remove and replace the brusses( carbon) by soldering. ok
Humm ...Didn't die before the accident? now dies? BMW has good mechanics,but could not find any problem???. I gota think that it is related to the rear ending,but how? I would look for loose connections, Battery Ground that might have been removed before welding.Battery terminals, Any primary connections that may not be making 100% contact . It's worth a try.Good Luck