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Electrical / alternator question

640 views 4 replies 4 participants last post by  IM QUIKR 
#1 ·
Electrical diagnosis is not my strong suit. My battery died yesterday. I mean died, no ability to hold a charge. Its a red top optima which I bought in 2011. I guess thats a good life span for a car battery. But here's my question. Knowing the battery has failed, I was able to drive over an hour on just alternator power. When I turned on my headlight switch from off to auto, the whole electrical system went dark for a breif moment. Dash lights went out, the radio stopped playing, etc, but then came back on. I did not try driving with the lights on. Do I assume its the alternator compensating for the power draw as the battery offered no buffer? Or should the alternator have been able to handle the extra load?

I have 195,000 miles on the original alternator 2001 IS300. Just curious if my battery is dead because of the alternator. Now that said. At idle with everything on, I get 14.3v which I believe is correct. I dont know what its doing at highway speeds but assuming its working enough to let me drive home.
 
#4 ·
The battery is really just there to compensate for major draws. Like starting the car.

Replace the battery first. Any other issues thereafter, have the alternator load tested.

The alternator in this car is a tank IMO.
 
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