2023 Tesla Model S Battery Size & Replacement Guide

As an ASE-certified master technician, I’ve seen the automotive industry shift dramatically over the past decade, and no vehicle embodies this shift quite like the 2023 Tesla Model S. Unlike traditional internal combustion engine (ICE) vehicles—and even earlier generations of the Model S—the 2023 “Palladium” generation Model S does not use a standard 12-volt lead-acid or AGM battery for its low-voltage system. Instead, Tesla transitioned to a proprietary 15-volt lithium-ion (Li-ion) auxiliary battery.

If you are looking for standard Cold Cranking Amps (CCA) or a BCI group size, you are going to be surprised. Here is everything you need to know about the low-voltage battery in the 2023 Tesla Model S.

Quick answer

• BCI Group Size: N/A (Proprietary Tesla Lithium-Ion form factor; much smaller and lighter than standard 12V batteries).
• Cold Cranking Amps (CCA): N/A. Electric vehicles do not have starter motors and do not “crank” an engine. The battery only needs to power the vehicle's computers, contactors, and accessories.
• Reserve Capacity: N/A in traditional minutes. The battery is approximately 6.9 Ah (amp-hours) and is constantly maintained by the high-voltage (HV) battery pack via a DC-DC converter.
• AGM vs Flooded Requirement: Neither. The 2023 Model S requires a specific 15V lithium-ion low-voltage battery.
• Terminal Layout: Proprietary multi-pin connector and specialized bolt-on terminals. It does not use standard SAE posts.
• Physical Dimensions: Significantly smaller and lighter than the Group 40 or U1 batteries used in older Teslas.
• Dual-Battery Setup: No. (The vehicle relies on one low-voltage Li-ion battery and one massive high-voltage traction pack).

Replacement battery options

Because the 2023 Tesla Model S uses a proprietary 15-volt lithium-ion architecture, you cannot simply go to an auto parts store and buy a standard Interstate, Optima, DieHard, Odyssey, or ACDelco battery.

• Tesla OEM Lithium-Ion Battery: Your primary and only truly safe option is the OEM replacement from Tesla. (Part numbers change frequently, but the lithium-ion module is typically ordered directly through Tesla Service or the Tesla app).
• Aftermarket Options: Currently, traditional aftermarket manufacturers do not make a 15V lithium drop-in replacement for the Palladium Model S. Do not attempt to wire a 12V AGM or flooded battery into this system; the vehicle's DC-DC converter outputs roughly 15.5V to charge the low-voltage battery, which will severely damage a 12V lead-acid battery and risk a thermal event or electrical failure.

Lithium-ion vs AGM vs Flooded — which does this vehicle need?

Older Tesla Model S vehicles (2012–2020) utilized standard 12V AGM batteries, which were notorious for failing every 1–3 years due to the constant, deep cycling required by the vehicle's sleep and wake cycles (Sentry Mode, OTA updates, etc.).

For the refreshed 2021+ Model S, Tesla engineered a 15V lithium-ion low-voltage battery. You absolutely must use the OEM lithium-ion battery. It matches the cycle life of the main high-voltage pack much better than lead-acid, theoretically lasting the life of the vehicle, and saves significant weight and space.

Post-installation relearn / reset procedure

Replacing the low-voltage battery on a 2023 Model S is much more complex than a standard vehicle and involves working near high-voltage components.

1. First Responder Loop: The high-voltage system must be safely isolated. This usually involves powering down the vehicle via the center screen and disconnecting the high-voltage interlock loop (First Responder Loop) under the hood.
2. Disconnecting: The negative terminal and the data connector on the Li-ion battery must be removed before the positive terminal.
3. Installation: Reconnect the positive, then the negative and data harness. Reconnect the HV interlock loop.
4. Relearn/Reset: Once the vehicle is powered back on, the Tesla vehicle computer typically recognizes the new module. However, you often need to access Service Mode (via the center screen) to clear any low-voltage battery degradation alerts and perform a software reinstall or gateway reset to ensure the battery management system (BMS) properly monitors the new Li-ion auxiliary battery.

Warning: Because of the high-voltage risks and software requirements, this replacement is highly recommended to be performed by a professional.

Signs of a failing battery

Even though lithium-ion low-voltage batteries are designed to last much longer than their AGM predecessors, they can still experience issues. Look out for:

• Software Warnings: The most obvious sign is an alert on the center screen stating, "Electrical system backup power is reduced" or "Schedule service to replace low voltage battery."
• Loss of Accessories: Sluggish window operation, unresponsive doors, or loss of interior lighting.
• Failure to "Start": If the low-voltage battery dies, the computer cannot close the high-voltage contactors. The car will be completely dead and unresponsive to your phone key or key fob, requiring a manual "jump" (supplying 12-15V to the jump leads hidden in the front bumper) just to open the frunk.

Common battery issues for this generation

The 2023 Model S Lithium-Ion low-voltage setup has largely solved the rampant 12V battery failures seen in older Teslas. However, common issues include:

• Software Glitches: Occasionally, a firmware update can cause the vehicle to stay "awake" longer than expected, stressing the DC-DC converter system.
• Jump-starting Confusion: Tow truck drivers and owners often try to jump-start the 2023 Model S using standard 12V jump packs. While applying 12V to the emergency release wires in the bumper will pop the frunk, trying to permanently run the 15V system off a standard 12V pack can cause electrical faults.

If you are experiencing low-voltage electrical anomalies or need to have your Tesla's systems diagnosed safely, don't leave it to chance. Find a trusted shop on Repairius.