LEXUS IS300h 12V battery problems/parasitic current

BogdanSpac · April 4

Hello everyone! About 2 years ago i have noticed that if i park my car (2018 Lexus IS300h Fsport) for about 4-5 days, the 12V Battery would die. I have replaced 3 12V batteries, and now it's time for the 4th one to be replaced. Everything was done at lexus, and they claimed that there were no issues with the car. Last week i went again to them, and they told me that they found an 0.154A parasitic current, which is 3 times more than it should be. They also told me that the operation to find the problem can take more than 3 days, and the price for this starts at about 600 euros because it is very complicated.

I am tired of throwing money at this car, cause every visit that i made to the dealership made my wallet cry, and i am getting almost tired of disconnecting the 12 V Battery after parking my car.

Do you guys have any suggestions or heard about this issue? I have tried to search on the forums but didn't found anything specific only something about a MPX-B fuse, but no solution.

Thanks!

ColinBarber · April 4

It can be time consuming to find the source of the issue, certainly to the point where it isn't worth getting a main dealer at £200 per hour to diagnose the issue. An auto electrician should be able to help.

You can DIY - you need to left a door open, but fool the car into thinking it is shut, then lock it and wait an hour for all the systems to sleep. Then you measure the voltage drop across the fuses to see which circuit is consuming too much power - then you can hopefully narrow down the problem. Typically it is stereos/amps, alarms or third party trackers/dash cams that cause the issue.

Here's the procedure to measure the voltage drop across the fuses. You shouldn't remove fuses - it can cause systems to wake which makes finding the issue harder.

NemesisUK · April 4

Curious ...

Were the batteries not replaced under warranty?

Your location is showing as Buckinghamshire but you quote the Investigation cost in euros?

You also say you are tired of disconnecting the Battery, how often do you do this? Each time you park up? Since when did you start disconnecting the Battery?

IS300FSPORT · April 4

I have been watching my 12v Battery like a Hawk. Installed a Victron 12v Battery Bluetooth monitor even after a long drive or after fully charging it using a Noco Genius 5 it seems to rest around 12.2v within 24 hours. Iv left mine 2 weeks straight without use & it starts up right away.

- How close is your key to your car when locked up its constantly sending a signal?

- Disable smart entry or put the key in a signal blocker pouch.

- Turn off your auto headlights?

- Any hardwired dashcam? Or other accessory

Recommend you Invest in a Noco GB40 JUMP START pack charged in the boot, you wont be left stranded again. If its left unused these batteries draining quick is normal due to low capacity 45AH is a small Battery.

keep us updated pls

BogdanSpac · April 8

First of all thanks for the replies!

ColinBarber, i tought about going to local reapir shop, and i will do so next week. I will also try the instructions that you gave me above, maybe this will get me closer to the root of the issue. Thanks so much!

NemesisUK, i am actually in Romania, Bucharest. I have bought the car back in 2020, and i noticed the problem soon after that, but everytime the dealer told me that it's either a problem with the Battery or that i don't drive often enough. Almsot 4 batteries later, they found out that there is a 154mA parasitic current. The batteries came with 1 year warrnity, but according to them, if they drop under x volts (can't remember exactly the number) the warrnity is voided. I disconnect the Battery everytime i know i won't use the car for several days, which often happens becaus i don't drive that much.

IS300FSPORT, what you have there looks pretty smart. I tried to look for the name of your device and it got me to a Remote Battery Disconnect Switch which would be more suitable for me, at least for now. I bought a 12V power bank, which saved me a lot of times. I have tried the things you said, beside disabling smart acces (i am not sure how do that), and the car is always parked far away from the keys.

I will continue my journey with the 12V Battery and i will come back here as soon as i get any news.

Thanks for the help and suggestions!