u/chuck415

I’ve been using the door lock automations every 3 hours with no issues for the past 3 weeks. Here’s my car sitting unused for 4 days and the 12V is currently at 12.58V.

My threshold to attach a battery maintainer to top off the battery is 12.55V, so I think I have another day or two before it hits that threshold.

Turning off the DCM/deactivating the car from the app is the surest way to stop the parasitic drain, but the door lock automations and charging schedule fixes are good temporary fixes if you want to keep connected services.

Here’s the door lock automation fix…

https://www.reddit.com/r/trailseeker/s/YQb3JlwfKn

Here’s the charging schedule fix…

https://www.reddit.com/r/Toyota_bZ/s/w595XbyYc4

And here’s how to deactivate your car and turn off DCM…

https://www.reddit.com/r/Toyota_bZ/s/o5mLYmHxXD

If you’re interested, I have a H5 AGM battery installed and I have the battery sensor disconnected from my negative terminal. Here’s my post on undercharging of the 12V battery if you want to learn more about it…

https://www.reddit.com/r/SubaruUncharted/s/fi8fg5TYa3

Here’s a technical service bulletin on all 2026 EVs that may cause an error message in the MID while DC fast charging. It looks like a software update will fix the issue.

TL;DR: The current 12V battery charging logic is taken from Toyota hybrids and undercharges the battery.

One fix is to remove the sensor on the negative terminal, which puts the system into a fail-safe charging mode and significantly improves charging of the 12V.

~

We've talked about the DCM/12V drain non-stop over the last few months, and I think we've landed on a few viable temporary fixes. Now let's talk about how the 12V battery actually gets charged, which turns out to be minimal under the current logic.

In an ideal world, the BMS would charge the 12V at 14.5V until current tapers down to 1A, then maintain a float charge around 13.5V to keep the battery fully charged and extend its lifespan. (AGM batteries want slightly higher voltages.)

Why is the battery undercharged?

The Uncharted/C-HR, bZ/Solterra, and Trailseeker/bZ Woodland all share the same DC-DC converter and 12V charging logic. A sensor on the negative battery terminal reports back to the car, which uses that reading to decide when to stop pushing charge voltage. In practice, it decides "good enough" almost immediately.

You can read more from u/andy_why, who identified the problem, documented fixes, and wrote a full write-up on it here:

https://www.reddit.com/r/prius/s/m8n8cn9Wxr

It applies to our EVs because we use the same battery sensor as the hybrids.

From Andy’s document…

“Is there any risk involved in using the fail-safe state?

No. The name “fail-safe” is exactly that - disconnection of the sensor is classed as a failure condition but one that reacts in a safe way and one that can operate indefinitely.”

Why is undercharging a 12V a problem?

Undercharging a 12V battery shortens its lifespan, often requiring replacement every couple of years instead of every five.

Cars with the DCM issue combine parasitic drain with undercharging, which can lead to a dead battery even if you drive daily.

The last two graphs show voltage drift when the car sits unused for 2–3 days — one with DCM off, one with the temporary door lock automation fix in place.

Voltage starts above 12.8V and drifts down to 12.5V. At that point, you need a full charge to bring the battery back to a healthy state.

Is the 12V battery charged while driving?

Not really. The first graph shows a day I drove from San Francisco to Bodega Bay, a roughly 1.5-hour drive each way.

On each drive, you'll see an initial voltage spike as soon as the car powers on into Ready mode. The 12V charges above 13.9V for a few minutes, then immediately drops to a maintenance/float voltage of 12.8V, regardless of the 12V's state of charge.

On the left side of the graph, you'll see voltage drift down to ~12.8V while the traction battery is charging. What you don't see is that the 12V gets charged above 14V for the first 10 minutes, before dropping for the rest of the session.

Ironically, the only time the car charges the 12V for an extended period of time is when in Ready mode and park. It will charge it for however long you sit in Ready + park at 13.9V. It may start off a little higher.

Disconnect the sensor to increase charging voltages

The second graph shows the difference when the current sensor is disconnected from the 12V's negative terminal. Same trip, San Francisco to Bodega Bay.

During driving, the battery holds a constant ~14.1V, whether your drive is 5 minutes or 90 minutes. That's still below the 14.5V for ideal absorption charging, but a big improvement over the 12.8V float you get with the sensor connected.

On the left of the graph, you'll see a constant float of 13.04V while the traction battery charges. For the first 30 minutes of that session, the 12V charges at 14.12V.

What does this all mean?

With the battery sensor connected, the 12V is chronically undercharged, which can shorten battery life and even lead to a dead battery, independent of any parasitic drain issue.

Disconnecting the sensor improves charging voltage, but you may still want a battery maintainer to keep the 12V at a full charge and get the most life out of it.

Another fix, per andy_why's write-up, is turning on your headlights while driving. This reportedly also holds charging voltage around 14.1V for the entire drive. I need to reconnect my sensor and gather data with the lights on before I can confirm it myself.

Has anyone else disconnected the 12V sensor, or driven with their lights on to charge the 12V? u/Maleficent_Lab4276 has done this, and he's the one who originally brought the sensor-disconnect idea to my attention.

Do I recommend disconnecting the sensor? No, but it definitely improves the charging voltages and I have yet to see any negative effects. Try it at your own risk.

I would test out turning on your lights (not DRL) to charge the 12V when driving. (See August 9th update below).

I would also recommend getting a cheap $30 battery maintainer like the NOCO Genius 1 to top off your 12V once a month or whenever your resting voltage drops below your threshold.

Update August 9, 2026:
u/chrischasesucks verified turning on the headlights (not DRL) does not increase charging voltage to 14.1V. This is probably only a hybrid workaround.

The more I research and read about overcharging, the more comfortable I feel keeping my sensor disconnected for normal daily use as well as long road trips with 6-8 hours of driving per day.

The only time I definitely wouldn't leave the sensor disconnected is in extreme heat. If the ambient air temperature is above 100°F (38°C) and you're driving for more than a few hours, I would recommend reconnecting the battery sensor.

As temperatures rise, the internal resistance of a 12V battery drops, which lowers its required float voltage. Feeding a continuous 14.1V for more than 3 hours in extreme heat can cause the liquid electrolyte in flooded batteries to boil off or dry out the glass mats in AGM batteries.

TL;DR: Instead of using eight door lock automations or the charging schedule method, you can stop the sawtooth drain with just one door lock automation.

First, I want to thank u/Altruistic_Film_8346 for sharing the discovery that you can stop the sawtooth drain with just one door lock, as long as you let the drain start first. Incredible find!

We don’t know why it works, but the sawtooth drain stops if you remotely lock the doors about 3 hours and 20 minutes after a drive. Since the drain starts a little over 3 hours after the car is turned off, any time after the drain begins you can stop it until your next drive by executing a door lock.

u/Altruistic_Film_8346 tested this over several days, and I’ve verified it over the past day. In the graph above (Ignore the sawtooth drain. I had a misconfiguration that prevented the Shortcut from running), my last drive ended at 12:29 on August 5. An automation remotely locked the doors 3 hours and 20 minutes after CarPlay disconnected, at 3:49 PM. After that, there was no sawtooth drain and no additional door locks for the next 20 hours. The last voltage dip on the right occurred when I manually unlocked the doors to retrieve something. There was no drain 3 hours after that door unlock.

I’d like to get more people to test this fix if you’d like to reduce the number of door lock automations.

(Edit: You can test this method out before spending time on shortcuts and automations, by setting an alarm or timer for 3h 20m after your last drive.

Look at your battery monitor graph and verify the sawtooth drain started, then lock your door. That should stop the drain.)

Maybe someone has an even better way to automate it. I’ve attached screenshots showing how to set up the automation.

Step 1: Create a Car Timer Focus
Create a new Focus mode (I called mine Car Timer) that doesn’t silence any people or apps. Also disable all options for the Focus.

Step 2: Create a Shortcut to Set the Focus for 3 Hours and 20 Minutes
Create a Shortcut that turns on the Car Timer Focus for 3 hours and 20 minutes.

The Show Alert action isn’t required. If you don’t want a confirmation message to start the timer, you can skip this action.

Use the Adjust Date action to add 200 minutes to the current date, then use Set Focus to turn on the Car Timer Focus until the adjusted date.

I named this Shortcut Rocky Lock Delay since my car’s name is Rocky. 😂

Step 3: Create a Remote Door Lock Shortcut
Create a Shortcut using the Subaru Connect/Toyota action to Remote Lock Vehicle.

Step 4: Create Automation #1
Create an automation that runs the Rocky Lock Delay Shortcut whenever CarPlay disconnects.

Step 5: Create Automation #2
Create another automation that runs the Remote Lock Vehicle Shortcut when the Car Timer Focus turns off.

Final Settings
- Disable Face ID in the Subaru Connect/Toyota app.
- Enable Background App Refresh for the Subaru/Toyota app.
- In Shortcuts, disable Show When Run.
- In Automations, select Run Immediately and disable Notify When Run.

If you make a trip with multiple stops and turn the car off several times, the timer automation will run each time CarPlay disconnects.

I included the optional Show Alert action in my timer Shortcut so I can confirm to run it and change my Focus. If the Shortcut runs multiple times, it simply extends the Focus end time, so the remote door lock won’t execute until at least 3 hours and 20 minutes after your most recent stop.

Let me know if you have any questions or if you come up with a better way to automate this fix.

Note: This automation will trigger a remote door lock at 3h 20m after CarPlay disconnect. If you interact with the car (open/close doors, unlock it, etc.) within the 3h 20m lock delay timer, the 3 hour sawtooth drain timer resets and you manually have to run your Lock Delay shortcut.

TL;DR: Instead of disabling the DCM, create a shortcut automation that remotely locks your doors every 2 hours and 40 minutes to prevent the parasitic 12V sawtooth drain from starting.

Background:
For those new to the 12V draining issue, read this summary…

https://www.reddit.com/r/trailseeker/s/BTkNH7tg1F

Here’s my documentation of the DCM/12V drain issue with video of the IR camera cycling on and off…

https://www.reddit.com/r/SubaruUncharted/s/Ai6lBiaSC6

Alternative Temporary 12V Fix:
I turned off my DCM on June 23rd because I was tired of monitoring the 12V battery. I haven’t had any sawtooth drains that occur about 3 hours after driving since deactivating my car in the Subaru Connect app.

u/Altruistic_Film_8346 discovered that you can prevent the sawtooth drain from starting by unlocking the doors, opening and closing a door, setting a charging schedule, etc. You just need to do one of these things within 3 hours to reset the sawtooth drain timer.

u/reasoned25 mentioned that you can create an iOS Shortcut to remotely unlock the doors and use automations to run them throughout the day.

Using this information, I created a Shortcut that remotely unlocks my doors when I’m home, since I prefer leaving my car unlocked in my garage, and remotely locks the doors when I’m away from home. You can keep it even simpler and create a Shortcut that just locks your doors.

I then created nine automations to run the Shortcut every 2 hours and 40 minutes. Using a 2-hour, 40-minute interval evenly spaces out the remote door locks while keeping the timer from reaching 3 hours.

It’s been over 48 hours since I reactivated my car in Subaru Connect and turned the DCM back on, and I haven’t seen the sawtooth drain pattern.

In the graph above, there’s a dip in voltage every time the doors are remotely locked or unlocked. The voltage recovers, but I’m losing about 0.02V each time the doors are locked. It’s not as good as having the DCM turned off, but a higher-capacity H5 AGM battery should handle the voltage dips from remote door locking much better. It’s definitely better than having a sawtooth drain(s) that takes the voltage below 12V.

I still need to monitor it for a longer period and test what happens while I’m driving when the doors are remotely locked. I think this is a promising temporary fix that stops the sawtooth drain while allowing you to keep connected services.

P.S. Make sure your automations are set to “run immediately” and the Subaru Connect app has Background App Refresh enabled, otherwise your automations won’t execute the shortcut correctly.

Update 1: If you don’t want to use shortcuts and automations, u/Altruistic_Film_8346 says you can use the car’s charging schedule events to trigger the reset. It’s the stop time that triggers it, so schedule short charging schedules that stops on the 2h 40m intervals. Physically plugging in your car is not required.

I didn’t want to mess with my charging schedule that is controlled by my EVSE.

Update 2: The automations don’t run while the car is in ready mode. You’ll get a notification in the Subaru/Toyota app that states, “That action cannot be completed while the vehicle is in motion or remote climate is on. Turn off remote climate or park the vehicle and try again.”

Update 3: After 3 days, I have not seen the sawtooth drain and voltage doesn’t drop below 12.5V after 12+ hours of rest.

I’ve switched the schedule to 8 automations every 3 hours to reduce the voltage sag. I think the sawtooth starts around 3h 5m after turning the car off after a drive, so testing this larger time interval.

I also ordered an H5 AGM 12V battery with 60 Ah capacity. It should handle the voltage draw better of the remote locking than the stock H4 45 Ah battery.

Update 4: After 6 days, the automations have been running as expected with no sawtooth drain using 3 hour intervals with 8 automations daily.

If you can’t get Shortcut automations to work, other people like u/Blu-ray have implemented the charging schedule method and have successfully prevented the sawtooth drain.

This YouTube video from a couple of months ago discusses the 12V battery issue that some of us are now seeing on the Uncharted and other cars on the platform — DCM parasitic drain combined with a small 12V battery.

https://youtu.be/m1L6g1qJDxg

It’s an AI video with a clickbait title, but it’s from an independent Toyota mechanic. It appears this has been an ongoing issue with Toyota hybrids and may have carried over to their EVs, since many of the components and software are shared.

I knew the older BZ4X had 12V issues and that was the reason I got a battery monitor within a week of getting the car, but I didn’t realize the hybrids had similar issues.

The main takeaways which many of us have already done:

- Monitor parasitic battery drain.

- If you mostly take short, infrequent trips, consider using a battery maintainer.

- Upgrade to a larger H5 AGM battery.

The stock battery is only 45 Ah. Most H5 (Group 47) AGM batteries are around 60 Ah. My previous car used an 80 Ah H7 battery, despite having fewer electronics drawing power while off.

The 2027 model year will come with a larger 12V battery, so it’ll be interesting to see what Toyota/Subaru chooses.

Regardless of the DCM drain, I plan to upgrade to an H5 AGM battery for the additional reserve capacity. The stock 45 Ah battery is undersized for a modern EV.

The State of Charge YouTube channel did a 70 mph range test on an Uncharted GT and got great results! Here’s the video…

https://youtu.be/8T\_LArUVvGE

255.1 miles of range at 3.8 mi/kWh

That’s more than I expected. Motortrend only got 236 miles on their 70 mph test.

I thought I had resolved my 12V battery drain issue by putting my key fobs in a Faraday box, but it only lasted a few days. I’m still seeing the sawtooth battery drain shown in the graph.

I’m starting to notice a pattern. About three hours after driving, the sawtooth drain begins and continues for 4–5 hours before the voltage stabilizes.

If the voltage consistently dropped to around 12.4V, I wouldn’t be concerned. However, I’m occasionally seeing a secondary drain that pulls it below 12.2V.

Is anyone else with a battery monitor seeing this same pattern?

I’m a low-mileage driver, averaging only about 13 miles per day, and I don’t charge very often. To maintain the 12V, I’ve been putting the car in Ready mode for an hour or so when there’s low voltage.

I’m guessing it’s a telematics/DCM module issue. The drain consistently starts about three hours after driving. Is anyone else seeing this?

Update June 13, 2026: As u/mrmao mentioned deactivating your vehicle from the Subaru Connect app will turn off DCM requests. I deactivated my car last night and didn’t get the battery drain 3 hours after driving or anytime in the last 12 hours.
I’ll continue monitoring to make sure the sawtooth drain is gone.

The Uncharted is now available across all trims in ABRP.

I found this good article on real world battery health. There’s nothing really new, but it’s nice to see data backing up findings and recommendations.

Toyota is conservative with their BMS and we have a large 12% battery buffer on our EVs, so I feel confident of minimal battery degradation.

The biggest takeaway for me is to limit the extremes SoC on low and high end.

From the article…

“State of charge (SOC): Utilizing the full battery

EV owners are often advised to keep their battery charge (SOC) between 20% and 80% to avoid the chemical stress associated with a full or empty battery. However, our data indicates that this cautionary measure is only critical if the battery is habituated at these extremes for extended durations. For typical daily use, strict adherence to the 20-80% SOC rule may be unnecessary. 
 
To measure the actual impact of charge levels, we analyzed how long vehicles spend at extreme SOC levels (below 20% or above 80%) across all states (driving, charging and rest). We categorized the vehicles into three groups:

-Low exposure (below 50% of total time at extreme SOC)

-Medium exposure (50%-80% of total time at extreme SOC)

-High exposure (above 80% of total time at extreme SOC)

The data demonstrates that moderate exposure to extreme SOC levels does not significantly accelerate degradation. The degradation rates for the low (1.4%) and medium (1.5%) groups are nearly the same.
 
However, there is a critical threshold at 80% exposure. Vehicles that habitually spent over 80% of their total time at extreme SOC levels experienced a significant acceleration in battery degradation, averaging 2.0% per year. This increase shows that battery degradation only accelerates when there is prolonged, habitual and extreme exposure to high or low states of charge. 

Why moderate SOC exposure is safe
A key factor in mitigating SOC-related stress is the protective engineering implemented by auto and battery manufacturers. All modern EV batteries incorporate hidden software buffers at the upper and lower limits of the charge capacity. For instance, a battery indicating 100% SOC is chemically less than a full charge, and 0% does not represent a chemically empty state.
 
This engineering buffer likely explains the minimal impact observed from moderate SOC exposure in our analysis. The battery is designed to handle normal use across its entire charge range.”

https://www.geotab.com/blog/ev-battery-health/

And here’s another good article discussing Depth of Discharge and its impact on battery life…

https://www.recurrentauto.com/research/one-simple-trick

“Through the first five months of 2026, the Solterra remains ahead with 4,919 units sold, followed by the Uncharted (1,792) and Trailseeker (1,483).”

Pretty good numbers considering they’ve only been available for 4-6 weeks. I’m curious to see Toyota’s numbers.

https://electrek.co/2026/06/02/subarus-new-evs-already-outselling-solterra/

I normally see a sawtooth drain pattern overnight, with the 12V battery dropping as low as 12.1–12.2V, not good.

I keep both key fobs about 28 feet away from the car and don’t use the digital key as our bedroom is above our garage.

The owner’s manual recommends keeping the key fobs and digital key at least 6 feet away from the vehicle to prevent 12V battery drain. I assumed 28 feet away and one floor up would be well outside the communication range.

On Saturday, I put both key fobs in a Faraday box after a drive, and the sawtooth drain disappeared! It’s now been over 40 hours since I last drove the car, and the 12V battery has remained steady at 12.55V. I haven’t seen it stay that stable for that long since installing the battery monitor.

Anyway, just wanted to let you know if you’ve had 12V battery issues and keeping your key fobs and digital key/phone close to your car.

I saw someone post on a 2026 Toyota BZ Facebook group that they used an OBDeleven 3 and its app to mute the interior reverse chime. It does appear they officially license with Toyota and they allow you to change dealer level settings.

On their support page, it states that Subaru only gets basic OBD2 support.

https://support.obdeleven.com/en/articles/5603309-does-obdeleven-support-my-vehicle

But I’m wondering if custom dealer settings will work on the Uncharted since it’s Toyota software. Has anyone used an OBDeleven 3 on their Subaru EV?

I’m paranoid about the 12V battery failures some people have reported with Subaru/Toyota EVs and other automakers, so I installed this ANCEL BM300 Pro battery monitor. It took less than five minutes to install.

It has notifications and alarms you can set if the battery drops below a certain voltage. It uses Bluetooth, so you need to be within about 10–15 feet of the car to get data, but it makes it easy to monitor your battery’s state of charge (SoC) through the app.

There will be times when we don’t drive the car for a few days, and I want to make sure telematics requests from the Subaru Connect app aren’t draining the 12V battery.

Other things I’m doing to avoid 12V battery drain:

- Disabled ACC mode
- Never use “Power On” mode (massive drain)
- Always use “Ready” mode if I’m sitting in the car waiting, so the traction battery charges the 12V battery

We got these two things that have been useful for our Uncharted. The first is a charger dock and hook to hang the cable. You can find it on Amazon too.

https://ev-lectron.com/products/lectron-tesla-nacs-electric-vehicle-charger-nozzle-holster-dock-j-hook-cable-management

The second one is this silicon charging mat for the wireless chargers. It’s thin enough that it still charges the phones that have silicon cases. It’s more for protection of the plastic charging area as I think our silicon cases are grippier directly on the charging surface.

https://www.amazon.com/Silicone-Wireless-Protective-Anti-Slip-Accessories/dp/B0D2D3DRGL

We got our Sport in Metropolis Gray a couple days ago and love it! Our dog approves too. 😂

We got a great deal, $7,500 under MSRP. We also couldn’t pass up the 0% APR for 72 months. It’s free money!

The car itself is great, but the buying experience with this dealer was not. I negotiated the OTD price over text, which was great. I got pre-approved for the loan and sent them everything they needed ahead of time, but it still took over three hours at the dealership before we finally had documents to sign.

They also prepped the wrong color car, which delayed our scheduled pickup time by a couple of hours, and they delivered the car with only 17% SoC. I had to figure out how to use a Tesla Supercharger before driving home.

If I had to do it over again, I would’ve gone with a different dealer that had better customer service. The extra $500 in savings wasn’t worth all the frustration during signing.