Hello everyone! I have some issues with the 12V battery on my 2018 IS300H. If I don't use the car for about 3 days, the battery dies. The dealership replaced the 12V battery but it didn't solved the problem. I also went to a battery shop and they said that the battery and the charging are good. They said that it is probably a parasitic drown. I don't have any aftermarket accessories installed. Has anyone experienced a similar problem? Thanks!

 

If you have a multimeter, you can perform a parasitic draw test yourself if you want, it's the exact thing they would do at any shop.

Two ways to do it: (1) remove the negative battery terminal, put the meter on amperage reading, and connect the meter to the battery post and the terminal so that the meter is tied between. This will give a reading in amps, and anything between 30-50 MilliAmp (0.030 to 0.050 on the meter) is considered in spec. Anything above that and you go to the fuse boxes and remove fuses one at a time and see if the number goes to that 30-50. You kind of need a wiring diagram to see what's on that fuse once you find the fuse that makes a difference however, as there's typically 2-3 items on each fuse.

The second way to do this is to leave the battery connected and go to the fuse boxes with your meter and perform a voltage drop on each fuse, that is, put your meter on volts and put them in the two metal pins on the back of the fuse. It should show zero until you get to a problem fuse, at which point it will show a very small voltage. There's tables online that translate the amount of voltage along with the size of the fuse into the amount of draw it's actually producing. Again you would need a wiring diagram to see what all is on that fuse.

Once the fuse is found and you have the items on that fuse, you would then have to go to each of those physical items and unplug them until the problem unit is found, and there's your resolution.

A couple of cautionary notes. Both ways require the car to be completely off, and if you use the meter between the battery way, do not turn the car on to anything at all especially try and start it, it'll blow the meter up. Second, I don't remember if the battery is in the hatch but if it is, you would need to leave the hatch open, but use a screwdriver or something to close the latch to give the car the impression that it's closed. Same for while your investigating the interior fuses, just close the latch of the door.

It sounds really dumb, but I have had people tow cars to me for this exact issue to find that the rear most interior light is on for whatever reason so make sure you look at the super obvious first.

- Shane

 

I don't know how to thank you for all this information. In the meantime, i already booked an appointment to the Lexus dealership in order to test it again. Before I hand them my car I will try to do all the things that you told me. Hopefully I don't mess anything up by doing all this measurements, but it's definitely worth trying because this issue has been stressing me a lot lately. After I find the cause I will post it in this thread, maybe it will help someone in the future.

 

All good my dude. It sounds super complicated, unfortunately I've done a ton of them so it's easy for me but it can be intimidating for others that aren't electrically inclined. As long as you don't connect the battery with the meter still hooked up it should be fine. And again, don't try to start it lol. And given it's a hybrid, one other word of caution is anything with an orange cable just don't mess with at all. Those are the high voltage lines and technically they don't have any voltage with the car completely off, but also 99.9% likely they have nothing to do with the draw.

Ultimately, if you're not super comfortable/confident, I would just say let the dealer do their thing. The last thing you want to do is create another issue and pay more for it in the end.

- Shane

 

I have been experiencing the same problems for about two years now. In the official garage told me that for the age of my car the battery should last for a couple of years more.
I had also problems with the infotainment that was rebooting every 10 sec. Only way of fixing it was either disconnecting the battery or removing the fuse.
My theory is that the infotainment standby/sleep mode is not always working properly. Then, when car is shut, the infotainment keeps draining current until the battery goes flat. If you take the car daily, the battery will last enough until the next charge. But if you don't drive for 3-4 days, then goes flat.