You have to ask yourself a few questions. Does your dad use the stop/start function? Does your dad have a cell phone module to remote start the vehicle? Then see if you have a `regular' battery or an AGM? If he does use stop start, and/or has a cell phone to remote start, he should have an AGM battery. Other than that you have to look for a short somewhere, or possibly a problematic alternator, or simply bad/dirty cable connections.

 

Thank you! Out of that list, the only thing he uses is the start/stop, but he dislikes it, and he has a regular battery. We'll try replacing it with an AGM one and see how that goes.
Do you happen to know if there is a permanent way to disable the stop/start? I read on my Accord forum that you have to manually disable Honda's stop/start before each drive- is that the same case for Toyota's?

 

There are also reports of leaving the auto high beam on draining the battery. If he uses the auto start/stop function on short trips the battery does not have time to recharge.

 

I also own a 2019 Toyota Highlander that has the auto start/stop function, which is designed to not turn on when the battery needs charging.
However, i also am having an issue with my car’s battery continually being dead when trying to start my car. It happened again last Thursday after driving over an hour and parking the car for 45 minutes. When I went to start it, the battery was again dead. It’s happened at least 5 times so far, and I even had it checked by the dealer at my last service.
They checked it and told me everything was fine.

 

Does he leave the key fob in the car? Sometimes that contributes to the battery draining from what others have mentioned/posted. Not sure if this applies to your dad.

 

This is what I was thinking. I always did this with my previous car for 10 years (just left the key in the car in the garage) and always wondered why the battery would die so easily. It wasn't until I got my next car and read the manual that I realized the transponder and security system turns "on" and activates when the key is near. Now, I keep my keys far away in the house, and I have no trouble.

 

"Since purchase, the battery has died twice, the first time was a few months ago, it was towed to the dealer, who installed a new battery. The second time was this weekend, my dad used a jump starter battery pack and it started right up after that."
So first battery lasted two years and the replacement 2 months correct?
If so return to dealer they should test the charging system and test for a parasitic draw.

Once this is ruled out then try some of the operational fixes that have been suggested.

 

"Since purchase, the battery has died twice, the first time was a few months ago, it was towed to the dealer, who installed a new battery. The second time was this weekend, my dad used a jump starter battery pack and it started right up after that."
So first battery lasted two years and the replacement 2 months correct?
If so return to dealer they should test the charging system and test for a parasitic draw.

Once this is ruled out then try some of the operational fixes that have been suggested.

That is correct. I was thinking parasitic draw too, but I figured I would check to see if it's a common issue first, before drawing conclusions. Thanks!

Yes you can buy this device off of Ebay, which was designed by someone right on this site:

Disable Toyota Automatic Stop Start Permanently Highlander Idle Stop HL3 | eBay

This WILL FIT ALL Highlander Models with Stop/Start Year 2017 thru 2019 Models. If you have a 2020+ Highlander See this link for our module for the 4th gen HL. This is a custom design just for Toyota Stop/Start Systems.

www.ebay.com

Thank you! Even if it turns out to not be the cause of the battery problems, he'd still love to have it disabled with this!

 

You might want to read the following article and have the dealer install the correct battery (I believe I saw somewhere in your post that you are using "regular " battery) ... You also mentioned that your dad likes to listen to XM, but didn't see if he drives local short distance etc. which can impact the battery from being charged fully... In general, regular lead-acid battery life shortens dramatically if allowed to run down to ~50% a few times...especially never fully charged.

EFB Battery Guide: Everything You Need to Know About EFB Technology

Reliable Power Delivered Worldwide

www.rbbattery.com

 

I recently had to replace the battery in my 2017 Highlander Limited. I did some casual battery research and decided that a AGM battery was the way to go. Fortunately the service advisor was sharp and let me know that a AGM battery is NOT the appropriate type of battery for my car. I ended up installing a EFB type battery. This is the correct battery for my Highlander. It has to do with "charging profiles". Using the wrong battery type will result in a dead/damaged battery. Do your research before you decide.
In addition to the above, I use a "battery maintainer" once a month. It's sort of like a smart charger. It not only tops off the charge, it cycles through charge/discharge. This de-sulfurizes the plates and keeps the battery in good shape. The battery maintainer can take most of the day to run it's program.
I do this because of the low amount of miles I put on each month. My Highlander would never get fully charged otherwise.

 

Do you need EFB or AGM Battery?| VARTA Automotive Batteries

EFB or AGM? Find out which battery suits your vehicle best ► Compare VARTA® battery technology for start-stop and high-energy vehicles.

batteryworld.varta-automotive.com

This says an AGM is a suitable substitute for an EFB.

5 Battery Types Explained - Sealed, AGM, Gel | BatteryStuff

Confused by all the different types of replacement batteries on the market? BatteryStuff clears it up for you with this guide on what’s right for your application.

www.batterystuff.com

Compare the charge profiles for flooded and AGM batteries. While the AGM profile is not good for the EFB, using an EFB profile on the AGM is within limits.

Research show that EFB is the choice for lower cost. An AGM battery will perform similarly to an EFB.

 

Just to give everyone an update and close out this thread- the problem's still officially unresolved. We disabled stop/start and the dealer checked the car again, didn't find anything unusual, no parasitic drain, no nothing. Battery has a good charge and the dealer did not recommend replacing it with any different type of battery. We keep a jumpstarter in the trunk and have to jump it every couple of weeks when it doesn't want to start, but it'll start right up once jumped. Not really what we expected from Toyota, but it certainly beats the problems of some other manufacturers. Rather than spend more time and energy trying to pinpoint the issue, we've decided to just live with it.
Thank you all for the suggestions, though.

 

Just to give everyone an update and close out this thread- the problem's still officially unresolved. We disabled stop/start and the dealer checked the car again, didn't find anything unusual, no parasitic drain, no nothing. Battery has a good charge and the dealer did not recommend replacing it with any different type of battery. We keep a jumpstarter in the trunk and have to jump it every couple of weeks when it doesn't want to start, but it'll start right up once jumped. Not really what we expected from Toyota, but it certainly beats the problems of some other manufacturers. Rather than spend more time and energy trying to pinpoint the issue, we've decided to just live with it. Thank you all for the suggestions, though.

I have the same issue. I leave my 2019 highlander parked for 2-3 days and I have to jump it. Did you ever resolve the issue? It has to be a drain.

 

Yeah, manually disable auto start/stop, that seems to improve the issue. We've openly had 1 dead 12V since we've been doing this.

We also keep a jumpstarter pack in the trunk, just in case.

 

Same problem here. No remedy yet. Manual says run car minimum 30’/wk. Lose about 20% battery charge overnight?

 

Same issue. 2018 Toyota Highlander. Happened once, AAA jumped, replaced battery right after jump with Costco recommended battery. One month later happened again, bought jumper box, and just dropped off Highlander with Toyota service. $175 for diagnostic, will update when they call back…

 

I have the same issue, I turn off the start stop function. And I only use the auto lights settings when I’m driving. I had the battery replaced even though the dealer said it was a good battery. Then I went to 7/11 for like 3 minutes in and out and when I came out it was dead. Then another time I had the start/stop function on and it died on me at the traffic lights. I brought it to the dealership and they told me it was good alternator was good. So now I always shut the start/stop function and I don’t leave the auto lights on anymore. From there I never had and issues. But I’m still wondering why is doing that and the dealership tells me everything is fine. All the electrical wires are clean. I check everything. 4 mechanics check it for me and the dealership like 5 times. And I’m using the correct batter. I got a 2019 Kia Stinger and I never have issues like that with it. I really love the Highlander but this is the only issue I have with it…….

 

Our 2017 highlander has this same random battery flat problem -just googling for answers

 

Try this as a first step to confirm there's a problem ...