2025 Tesla Model Y Low-Voltage Battery Size & Specs

As an ASE-certified master technician, I see a lot of confusion when it comes to the low-voltage auxiliary batteries in modern electric vehicles. When discussing the 2025 Tesla Model Y, the conversation shifts drastically from traditional internal combustion engine vehicles. If you're looking for standard specs like Cold Cranking Amps (CCA) or BCI group sizes, you’re in for a surprise. Starting in late 2021 and carrying through to the 2025 model year, Tesla ditched the old 12V lead-acid setup in favor of a modern, proprietary 16V lithium-ion low-voltage battery.

Here is everything you need to know about the 2025 Tesla Model Y low-voltage battery.

Quick answer

• BCI group size: N/A (Tesla uses a proprietary 16V lithium-ion battery, replacing the older Group 85BLS / 51R used in 2020–2021 models).
• Cold Cranking Amps (CCA): N/A. Electric vehicles do not have starter motors, so CCA is irrelevant. The battery powers the MCU (Media Control Unit), lighting, windows, and contactors.
• Capacity: Approximately 6.9 Ah (roughly 100 Wh at 16 volts).
• AGM vs flooded requirement: Neither. It is a strict 16V Lithium-ion (Li-ion) battery.
• Terminal layout: Proprietary multi-pin data and power connector blocks, not standard SAE posts.
• Physical dimensions: Considerably smaller and lighter than a standard 12V battery (roughly 8" x 3.5" x 6").
• Dual-battery setup: No, a single low-voltage pack sits under the HEPA filter housing in the frunk area.

Replacement battery options

Because the 2025 Model Y utilizes a highly specialized 16V lithium-ion pack managed via Tesla's internal LIN bus, you will not find standard aftermarket replacements. Traditional heavy-hitters in the battery market have not yet produced drop-in replacements for this specific 16V architecture.

• Interstate, Optima, DieHard, Odyssey, ACDelco: Currently, none of these manufacturers produce a compatible 16V lithium-ion battery for the 2025 Model Y.
• OEM Tesla (Part # 1622967-00-A or superseding numbers): If your 16V battery fails, you must purchase the replacement directly through the Tesla Service Center or via the Tesla app.

AGM vs flooded — which does this vehicle need?

The short answer is: neither.

Older generation Model Ys (built before the AMD Ryzen MCU update in late 2021) utilized a traditional 12V lead-acid battery (usually an AGM). However, the 2025 Model Y’s electrical architecture is designed entirely around a 16V lithium-ion power supply. Attempting to retrofit a 12V AGM or flooded battery is physically impossible due to the proprietary harness, and electrically incompatible. The vehicle's high-voltage DC-DC converter outputs around 15.5V–16V to keep this Li-ion pack charged.

Post-installation relearn / reset procedure

Unlike a BMW or Ford that requires a scan tool to register a new battery, the Tesla Model Y handles the relearn process via its own software.

1. Disconnect the First Responder Loop: Before replacing the battery, you must power down the vehicle and disconnect the high-voltage loop under the hood, followed by the low-voltage harness.
2. Swap the Battery: Unbolt the bracket, disconnect the proprietary data/power plug, and swap the new 16V unit in.
3. Reconnect: Reconnect the low-voltage battery, then reconnect the First Responder Loop.
4. System Check: The vehicle will wake up. You may need to perform a scroll-wheel reboot (hold both steering wheel buttons down until the screen turns black and the Tesla logo appears) to clear any lingering electrical fault codes.
5. Software Update (Optional): In rare cases, if BMS (Battery Management System) errors persist, running a software redeploy via the Service Mode menu will force the vehicle to recognize the new hardware.

Signs of a failing battery

Even though lithium-ion auxiliary batteries are designed to last the life of the vehicle, failures can still happen. Watch for these symptoms:

• On-screen warnings: The most common sign is a persistent alert on the MCU stating: "Electrical system backup power is reduced – Vehicle may unexpectedly lose power" or "Schedule service to replace low voltage battery."
• Software updates failing: The car will refuse to install firmware updates if it detects a weak low-voltage battery.
• Loss of accessory power: Windows, doors (which use electronic latches), and the power liftgate may become unresponsive.
• Dead vehicle: If the 16V battery dies completely, the high-voltage contactors cannot close, meaning the car will not drive, wake up, or even allow you to open the doors without the manual emergency release.

Common battery issues for this generation

The switch to the 16V lithium-ion battery largely cured the infamous "dead 12V" issue that plagued older Teslas. However, the 2025 generation can still experience issues with the battery’s internal BMS board. Because the lithium battery has its own integrated management computer, a software glitch within the battery itself can cause it to isolate from the vehicle's network, resulting in a sudden loss of auxiliary power. Additionally, deep-discharging the main high-voltage pack to 0% can permanently damage the 16V battery, as the DC-DC converter will shut off and leave the 16V battery to drain completely.

If you are experiencing electrical gremlins or need help safely accessing and replacing components on your EV, don't risk a high-voltage mistake. Find a trusted shop on Repairius.