This is my first time ever posting on a forum but I’ve been doing a lot of research and I found others with this and the solutions didn’t seem to help me.

one day my girlfriend was driving her 2007 Lexus IS250 and the battery light came on. So I drove it to the local auto zone and got it tested and they said that my alt wasn’t holding charge. I bought the new alt and went home and replaced it. Only thing I can remember I might’ve did wrong was plug the battery up to pop the trunk while the alt was out. I ended up putting the alt in minus that hard bracket on the back on, but the car didn’t start. All lights come on like regular but no crank and when you press the button they cut off then come back on. After checking connections and fuses I read it could be the fusible link so I replaced that. Car still doesn’t start and still does the same thing. Now the battery has gone dead so I bring it to auto zone who say it’s a good battery charge it. And I try everything again but the same result. Next morning batteries dead again. So Now I brought it to o’Reily’s and the tell me it’s bad. I go buy a new battery from Walmart put it in and the same thing happened. I don’t know what to do at this point anything will help

 

So you're saying that each time you install a known GOOD battery that it is becoming drained overnight?

So when you replaced the fusible link, did you find out whether or not the previous one had blew?

 

An alternator consumes electrical current, which generates magnetic fields and makes it spin - that starts a car. It also can do the opposite, and generate electricity from the running engine. Alternators, however, do not “hold” electrical charge.

Battery does not go dead unless you leave the car in a state other than “everything is off”... or unless there is a severe current drain when it is off (which is not normal for the car, since clearly before it worked just fine, and it drove normally before without losing battery charge in one day.

I am not sure you know what you are doing. I am wondering if in your attempt to fix it, you actually fried some electronics in the car by connecting the cables incorrectly. If you have a multimeter, you can measure what the voltage is on the battery, when everything is off. If it is too low, the car wont start.

 

not since I put the brand new battery in yesterday. Now it just cuts on and all lights go off when trying to start.

The old fusible link didn’t appear to be blown but I still went through process of elimination.

 

I’ve never worked on a Lexus before every other alt I’ve done was pretty straight forward. I’ll test it now and give you numbers.

 

Honestly, from your description, it sounds like either a battery is half dead and when you proceed to crank the car, it dies because there is not enough power. But also, it might be that something was not hooked up correctly, which creates a problem once you start cranking it.

 

I just replaced the alt on my 06 IS350 with 130K miles, reconnected the battery to get something out of the trunk like you, and had the exact same problem when I went to start it. Did you ever figure out what it was? I really don't want to have to take this thing into an electrical shop, or worse the dealership.