I'll give the whole picture first. 2007 Lexus IS 350 not really any big issues ever, haven't really added anything to it aftermarket.. Got dash replaced via warranty(sun damage) and a few days after I got it back I pull up to a QT no signs of issue - walk in get a drink and come back out. Touch handle to unlock car unlocks and beeps several times(6-8) normally does 2. Car is pretty much dead and won't start.

Great, thinking it's a dead battery. Try to get a jump from a V8 Truck, no luck(cables get hot? cheap?). Then a AAA person happens to be walking in and kinda starts helping out. He brings his portable charger over and jumps the car and it starts. Unplugs and it dies - so we're thinking dead alternator. He tries a few things to just kinda get me on the road and home(Charge via truck, jump etc) His portable jump box is about 25% so not sure if we'll make it home. Decided to give it a shot and made it home AND the battery was charged as well as his portable charger. So we assume it's something odd going on since the alternator obviously charged it.

I went ahead and bought a portable charger as well only mine won't stay connected as it's too big and has short cables. I then take it in to Lexus and ask them to check wiring from where they replaced dash - but at this point it's working so I doubt they checked much, if anything.

Fastforward 6 months. Yesterday I head to my car to go to lunch, no signs(dimming, etc) prior. Door won't unlock, trunk won't open, have to use manual key. Car is 100% dead. So I'm thinking battery or alternator again. I jump with my portable and it starts, but dies when I unplug. I take battery out and to Lexus, they replace it.(was only from April last year)

I then take it back to my car put it in and it starts fine, so I'm thinking alternator could still be bad but not quite sure. So I turn it off to finish up work and 30-45 minutes later come out, 100% dead(I made sure to turn everything off first including lights). Doors won't unlock, trunk, etc. Try to get jumped off but it's the same again. Portable battery is a bit too low at this point so I take it home overnight and charge.

Fastforward to this morning, jump off with portable kit, starts fine. Read voltage and it's only what the portable jumper reads, sure enough I unplug it and it dies. (So I'm wondering if alternator is being drained too much to a dead battery or also isn't working?) Then measure battery after I take the jumper off and it's reading 0(not sure how accurate that is now?)

So at this point I'm testing a theory that there is a drain by charging the car battery outside of the car(if it will) and starting, driving around, then removing the negative while it sits and see if it will start again later.

TL;DR- Car won't start and killed a brand new battery in <1 hour of not running. Is it a relay or something or can bad alternator do that? Any other options/opinions?

 

If you get a bad electrical smell from underneath the hood next to alternator? If you haven't changed the alternator that is my guess. Cause after you charge the battery it die. Meaning that it not charging on it own from the alternator.

 

Nah no smell that I've smelled. Thing is the battery was full, I only ran it for 2 minutes. and it was fine. It sat for 45 minutes (turned off) and then was dead.

 

Like i stated without the alternator working it won't charge your battery while it running. Even at a full charge it will die cause your alternator not charging it to keep it running. Its less then a $200 part and 2-3hrs of your DIY time if your handy. Other wise dealer gonna charge you a lot more probably close to $1000.

 

Yeah I am probably going to replace it regardless - but I don't think that's the only issue.

Like I said I started it (brand new battery) one time, for 2 minutes. That shouldn't ahve killed a full battery, not only to like 11 or 10 volts, but COMPLETELY dead.

 

Auto parts stores can check the alternator for free with it still in the car. Probably a good idea before dropping $ for a replacement.

 

Problem is getting it there lol, did find a 10A+ draw while car is off though. Not sure what it's coming from. But I took the fused link out of the circuit and that removes it.

 

Sorry to hear you continue to have these issues. But like you mentioned, you might wanna go ahead and throw in a new alternator to just eliminate that from the equation. If you need a hand and are still in the Greenville area, LMK! I've done the ALT in my IS350 before.

Is there ANYTHING aftermarket in/on your car? Even so much as a radar detector or USB-charging device.

 

your symptoms sound like a parasytic draw.
you say you have something that pulls 10 amps of current with car off?
if so then yes that is why your car battery is dying.
what "circuit " is this on?
how did you come to finding that you have a 10a draw?
you pulled fuse link? what does this fused link called?

this happend after lexus changed your dashboard? after the time you had it jumped by the AAA guy and you said fast forward six months later did it ever happen in that six month time period?


need more info.

 

I am having similar problems. Something keeps draining my battery. I got a new battery and a new alternator and still, my battery is dying.....I will be driving and then the inside lights start flickering before they go off.....then headlights go out and car is slowing down as well and then it dies.

 

Did you do the work yourself, or shop? If the latter then have the shop look it over. The battery is just responsible for starting the car. After that the alternator takes over. If its not working correctly then you'll have what you're experiencing.

What brand alternator was it replaced with?