I’ve had the car for about 2 and a half years and last summer my battery died. Took it to dealer and they said it was a bad battery. Changed it and couple weeks later battery dies again. Only aftermarket parts that are electrical in any way is 1.) Airlift suspension 2.) Exhaust cutout(vacuum actuated) 3.) interior dome lights 4.) fog lights. The new battery has died about 3-4 times already and I’ve been using a multi meter to check battery voltage and for a draw. The draw starts at roughly 1 amp but goes down to 0.03 after 30 seconds. Which makes it more confusing.
You should wait up to a half hour for all computers/modules to go the sleep before checking for a parasitic current draw.
Tester
Tis a good point. I’ll try that. Also the battery level after driving tends to be consistently at 12.35 volts for the past couple times I’ve checked. Next morning it was 12.03.
This indicates a bad battery or the battery charge is not being maintained by the charging system.
Plug this car battery monitor into your cigarette lighter.It will tell you what is going on with your charging system in real time.
I’d start w/the standard battery alternator voltage test. Before first start of the day the battery should measure about 12.6 volts. Immediately after starting the engine, 13.5-15.5 volts. Tell us what you measure on your car.
If that checks out ok, next is a parasitic drain test monitoring the current flow in the negative leg of the battery connection (with everything off). To avoid resetting the computers, ideally you’d want to insert the amp meter into the circuit without disconnecting the battery. I’ve never tried that, but I imagine its possible to use jumper wires to keep the battery connected to the car’s electrics while you insert the amp meter into the circuit. You’ve have to figure out a way to continually monitor the amp meter overnight of course. It might go to down to 30 mA after turning stuff off, but in an hour when you aren’t looking go back to 1 or more amps. There are cell phone apps that allow you to program it to take a photo every 5 minutes, maybe something like that.
Problematic door, hood, trunk, glove compartment switches are a common cause. As well, alarm systems and aftermarket electrics, especially aftermarket audio systems.
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And pop the hood right after you turn it off, then get any keys away from the vehicle. Those cars wake up if the key is nearby.
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I’d suggest that one is the primary culprit. #2 would be my next suggestion. Not sure why interior dome lights would be aftermarket… LED bulbs maybe? If it is more than that and connected to the car in ANY way outside the dome light circuit, assume that one may be issue as well.
Unplug the fuse for the suspension overnight and see if that fixes the problem. If it does… that’s the problem. If not, move to the Exhaust cutout and then the dome lights and then the fogs. I doubt it is a factory electrical problem at 4 years.
Well the airlift was installed March 9th 2019 and my battery first died August 23rd 2019. Cutout was June 11th. So honestly none of them really makes sense. But yeah I’ll have to try unplugging those one by one.
How much should a normal battery’s voltage typically drop in a 24 hour period? At night the temperatures about 37-40 degrees. This early afternoon my battery was at 11.9(23 hour period). I drove it around for a bit and after I parked it was at 12.4.
You are assuming a quality airlift system was installed. I am not. Your timeline screams out loud that the airlift system is to blame. Either a poor system or poor installation. Test it and prove it one way or another.
Doesn’t the timeline show a 4 month period until the battery started draining? My installer said the power to the airlift system is connected with the ignition so it shouldn’t be able to do anything unless the car is on. I will still check it anyway.
When you first turn your car off from a drive, the battery should read from 12.6 to 12.8 or maybe a little higher. If thats not the case, than you have a battery that’s not able to charge completely or the charging system isn’t charging properly. After letting it set overnight, the surface charge will be gone and a healthy battery will read 12.6 volts. Even with a parasitic draw a healthy battery will charge to 12.6 volts. After you confirm your battery is healthy and the charging system is functioning properly, then would be the time to check for parasitic draw. My first suspicion would be the air lift system pump turning on when it’s not supposed to.
I recently had a battery that tested borderline. It charged to 12.4 and worked great. But f I let it set two days the van wouldn’t turn over. I did a parasitic draw test and passed. Replaced the battery and all is well.
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Concur, measuring the battery at 11.9 volts, assuming it was fully charged then 24 hours of non-use, that’s too low. It indicates something is wrong. Hard to say what it is without more data. Most likely either the battery, the alternator, or parasitic drain.
I originally took it to the dealer and they said the alternator was good so I got a new battery. It’s only been a month or two with the new battery with the issue continuing. So I’m leaning towards a parasitic drain
Any current flow from the battery can be easily measured. The only exception is current that flows internal to the battery, or across the battery case. But those can almost certainly be eliminated here as a cause b/c the battery is new. The next step is simply measuring the parasitic draw over a 24 hour period.
We’ve got the same problem with our 2008 IS250.
The battery and alternator are fine, so we had an electric specialist come and have a look. We learned that there’s a parasitic drain from the onboard body control module which is discharging the vehicle when it’s switched off. The body control module also powers the audio module which is another item that can sometimes have this parasitic drain problem.
Either way it needs repairing or replacing and ‘regular’ garages don’t seem to have the software or coding skills needed to fix it. So it will have to go to Lexus & that’s going to cost a lot! 
Has anyone managed to remedy the problem? If so, how and how much did it cost?