Last month I replaced the battery in my 2013 GS for the third time. It had sit unused for 3 days. Today it wouldn't start and the battery measured 2.6V. With that low voltage I'm inclined to think that the alternator or some aspect of the charging system is the problem rather than the battery. Any suggestions on how to start troubleshooting this problem? BTW, I'm not aware of anything left on to deplete the battery and even if there was I can't imagine it getting that low. I have an multimeter but it only measures AC amps.
Thanks for any help.

 

Search on YOUTUBE "Parasitic draw test". Batteries don't go dead that quickly. Something is drawing power while the vehicle is idle.
Also, I believe there may have been issue with older GS & their ECU causing dead batteries. Not sure though, maybe look into that as well.

 

Have you replaced your networking module ECU? Check the TSB below and post of my replacement.

TSB: https://static.nhtsa.gov/odi/tsbs/20...86305-5448.pdf

https://www.clublexus.com/forums/gs-...l#post10785849

I haven't had a single issue since that replacement, and the car has been idle for many weeks at a time due to covid.

 

Use a second car, with jumper leads, or a lithium ion jump starter like Noco or Gooloo etc to jump start your engine.



Do you have a multimeter?



Switch the multimeter to voltage mode.
With the engine running, the red probe to red positive terminal of battery, and the black probe to the negative terminal of battery.

With engine off, a good battery would have 12+ volts.
With engine on, the voltage should be 13 to 14 volts - and this shows that alternator is charging battery.
​​If only 12+ volts, then you may have a faulty alternator.

If alternator test is good, then something may be draining battery, however this is extremely rare.
Faulty alternators are common.

 

Thanks everyone for the feedback and suggestions - esp the TSB link RE: the ECU module. Obviously I don't have the equipment mentioned to do the complete parasitic draw tests and am considering just replacing the ECU module and see what happens. Looks like the best price for a new one is about $95.

 

My wife just informed me that she cannot find her key fob for the car. A quick search failed to find it in the car. If it's in there, could that be causing the battery draw?

 

No. you won’t be able to lock a key in the car.

 

You can definitely lock a key in the car by using your second key fob.

 

Rephrasing my question a different way, would a Lexus key fob left inside the car cause a parasitic draw on the battery?

 

Highly unlikely.

Are you sure you have a parasitic drain?
Are you sure your alternator is charging the battery in the first place???

Over the past 40 years, I have replaced a number of alternators esp in Honda Accords, Benz V6 and Lexus ES.
However, I have never ever encountered parasitic drain.

 

I noted 13.6 V with engine idling and 12.2 after being off for 30 mins. Is that enough to say the alternator is working or should I take it in for further testing?

 

Your alternator is working with 13.6 VDC at the battery with the engine running.

What, if any, non-OE add-on equipment do you have that is powered by the car's electrical system?

You may indeed have one of the Lexus/Toyota vehicles with the defective printed circuit board (PCB) solder joint that caused a parasitic draw enough to kill the battery pretty quickly.

 

Yes, sounds like your alternator is fine.

 

I owned a Lincoln LS a few years ago. When the alternators went bad, they would still charge, but would drain the battery in 1 day while sitting. I always thought it was the strangest thing I had ever seen.

 

True.
You've refreshed my memory.
OP, you better take your GS to have the alternator checked out.
I remember last year, my ES was charging to 13.6 V etc with the engine on, but in the end, I got a brand new OEM alternator, because a good alternator should be charging >14 Volts.