My Lexus RZ's 12V battery keeps dying. Is it the DCM?

Short answer: If your RZ's 12V battery keeps going flat, ask the dealer for an overnight parasitic draw test. Dealers have found the DCM, the car's cell modem, not going to sleep. One owner got a Lexus software update plus a new 12V battery. Until it's fixed, cut back on app check-ins, disconnect third-party apps, and keep a jump pack in the car.

Symptom: The car won't power on or unlock, or the 12V battery is dead after sitting, even though the main battery has plenty of charge. It may happen again weeks after a new battery.

What to check first

1. Ask for an overnight parasitic draw test with the car sitting, not a quick battery test.
2. Ask whether your car is eligible for the DCM software update.
3. Disconnect third-party apps that connect to the car.
4. Keep a jump pack. Learn where the 12V jump points are in the owner's manual.
5. Run your VIN at nhtsa.gov/recalls.

Likely causes

1. DCM not going to sleep (parasitic drain). The DCM, or Data Communication Module, is the car's built-in cell modem for the app and connected services. One dealer measured a drain of about 2 amps with the car off, which fell to 30 milliamps when they pulled the DCM fuse. A healthy car should draw only a tiny amount when parked.
2. Third-party apps waking the car. Owners suspect apps that poll the car often, such as charging or trip-planning apps, keep it awake and drain the 12V.
3. Weak 12V battery after repeated drains. Each time a 12V battery goes fully flat it loses some life, so a battery that has died a few times may need replacing even after the drain is fixed.

What it usually costs

Owners report the 12V replacements and testing were done under warranty.

Is it safe to keep driving?

It's not dangerous while driving, but it can strand you. If the car is dead, use a jump pack or call roadside assistance.

DIY or shop?

Jump-starting and apps are DIY. A draw test and software update are dealer work. An EV's high-voltage system can stay live with the car off. Leave the orange cables, the big battery and the charging hardware to a trained EV technician.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists these recalls touching this area of the Lexus RZ: 25V577000 (2023-2025 model years, visibility:defroster/defogger/hvac system); 26V393000 (2026-2026 model years, electrical system:propulsion system). Check your VIN at nhtsa.gov/recalls. If your car is part of this recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 9 keyword-matched complaints for Lexus RZ 2023–2026 (of 24 unique complaints queried, NHTSA complaints API by model year, queried 2026-11-01; keywords: 12 v, battery, dead, drain, won t start, dcm) (NHTSA returned no data for 21 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 12V battery discharge - cause identified? on Reddit r/LexusRZ, an owner whose new RZ had killed its 12V battery several times got the dealer to keep it over a weekend. The tech saw a 1.6-2 amp draw, pulled the DCM fuse, and the drain dropped to about 30 milliamps with the battery still at 12 volts the next day. Others with the same problem followed the thread hoping for a fix.
• In Lexus RZ 12V/DCM software fix — my car received an engineering OTA update on Reddit r/LexusRZ, the same kind of case: after a dead 12V and an overnight draw test, an owner said Lexus engineering pushed a targeted over-the-air software update for the DCM drain and the dealer replaced the 12V battery. The dealer documented the drain dropping from about 80 milliamps. Other owners shared a workaround of setting a repeating charge schedule, and said a formal bulletin hadn't been published yet.
• In 2026 RZ Owners - is the 12V battery drain issue still a big problem? on Reddit r/LexusRZ, a buyer picking up a 2026 RZ 350e asked if the drain is still a problem. Several 2026 owners said they hadn't had it, including one with a June 2026 build. One owner suggested not using the app more than needed and skipping third-party apps that connect to the car.

Quick tip

Push for the overnight draw test. A battery that tests fine at the counter tells you nothing. The drain only shows up after the car sits.

Vehicle focus: Lexus RZ 300e, 350e and 450e, 2023-2026.

Safety / mechanic note

Jump-start only from the 12V points shown in the manual. Verify with a mechanic.