2020 Tesla Model S 12V Battery: Group Size, CCA, and Replacement Guide

Quick answer

• BCI Group Size: Group 51R
• CCA Rating: 400-500 CCA (approximate, specific to 12V battery)
• Reserve Capacity: 60-90 minutes (approximate)
• AGM vs Flooded Requirement: AGM (factory original is AGM, highly recommended for replacement)
• Terminal Layout: R (positive on the right, when looking at the battery with terminals facing you)
• Physical Dimensions: Approximately 9.375" (L) x 5.0625" (W) x 8.8125" (H)
• Dual-Battery Setup: Not applicable (Tesla Model S uses a single 12V auxiliary battery, in addition to the high-voltage traction battery).

Replacement battery options

The 2020 Tesla Model S utilizes a 12V auxiliary battery that is crucial for powering the vehicle's low-voltage systems, including the infotainment, lights, door locks, and initiating the high-voltage contactors. While the high-voltage battery powers the drivetrain, the 12V battery is essential for the car to "wake up" and operate. Due to the vehicle's sophisticated electronics and power management, an AGM (Absorbent Glass Mat) battery is the recommended, and often required, replacement.

Here are some popular replacement options for the Group 51R AGM battery:

• Interstate: MT5-51R AGM (check for specific Tesla-compatible part, as availability can vary)
• Optima: Optima YellowTop DH5-AGM (may require a spacer or fitment verification as Optima batteries can have slightly different dimensions)
• DieHard: DieHard Platinum AGM Group 51R (check availability and specific part numbers)
• Odyssey: PC1200LMJ-A or ODC-AGM51R (verify exact fitment and terminal orientation)
• ACDelco: ACDelco Gold 51RAGM (check for current part numbers)

Always verify the specific dimensions and terminal configuration against your vehicle's requirements before purchase.

AGM vs flooded — which does this vehicle need?

The 2020 Tesla Model S requires an AGM (Absorbent Glass Mat) battery for its 12V auxiliary system. The factory-installed battery is an AGM type, and switching to a traditional flooded lead-acid battery is strongly discouraged. AGM batteries are sealed, maintenance-free, offer superior vibration resistance, and can handle the deep discharge cycles and complex electrical loads characteristic of a Tesla. They also recharge faster and have a lower self-discharge rate, which is beneficial for vehicles that may sit for periods.

Using a flooded battery could lead to premature failure, issues with the vehicle's electrical system, and potentially void warranties. The vehicle's charging system is specifically calibrated for AGM battery characteristics.

Post-installation relearn / reset procedure

Unlike traditional internal combustion engine vehicles, the Tesla Model S does not typically require a complex "relearn" or "reset" procedure for the 12V battery after replacement. However, it's important to follow these steps:

1. Proper Disconnection/Reconnection: Always disconnect the negative terminal first, then the positive. When reconnecting, connect the positive terminal first, then the negative. This minimizes the risk of short circuits.
2. Allow Vehicle to "Sleep": After connecting the new battery, close all doors and trunks and allow the vehicle to sit undisturbed for a few minutes (e.g., 5-10 minutes). The car's systems will automatically recalibrate and power up.
3. Check for Alerts: Once the car powers up, check the touchscreen for any warning messages or alerts related to the 12V battery or other systems. If any persist, it may indicate a problem with the installation or the new battery.
4. Drive Cycle (Optional): Some owners find that driving the vehicle for a short period helps the car fully recognize and integrate the new battery into its system.

It is crucial to note that performing a 12V battery replacement on a Tesla involves working with high-voltage systems. While the 12V battery itself is low-voltage, care must be taken to avoid accidental contact with or damage to the high-voltage lines or components. Consult your owner's manual or a certified Tesla service center if you are unsure.

Signs of a failing battery

The 12V battery in a Tesla Model S can fail gradually, or sometimes quite suddenly. Here's what to look out for:

• "12V Battery Needs Service" Warning: This is the most obvious sign. The car's system constantly monitors the 12V battery and will display this message on the touchscreen if it detects an issue.
• Sluggish or No Door Handle Presentation: If the door handles don't present immediately or only partially when you approach the car.
• Intermittent or Non-Responsive Infotainment Screen: The large central screen may flicker, freeze, or fail to power on.
• Failure to "Wake Up": The car might not respond when you try to unlock it via the app or key fob, indicating the 12V battery can't power the low-voltage systems.
• Warning Lights (Non-Specific): Other seemingly unrelated warning lights might appear due to low voltage affecting various electronic control units.
• HVAC Issues: Problems with climate control or fan operation.

Don't ignore a "12V Battery Needs Service" warning. While you might have some time, it can quickly lead to a no-start condition.

Common battery issues for this generation

The 2020 Tesla Model S, like other Teslas, relies heavily on its 12V auxiliary battery for critical functions. Common issues for this generation often revolve around:

• Premature Failure: Some owners have reported that the original 12V battery may fail sooner than expected, sometimes within 2-3 years, depending on usage patterns and environmental factors.
• Parasitic Drain: While Tesla's software manages power consumption effectively, problems with modules or "vampire drain" can still stress the 12V battery, especially if the car is parked for extended periods without being plugged in.
• Software Updates: Occasionally, a software update can impact 12V battery management, though Tesla usually addresses these quickly with subsequent updates.
• Extreme Temperatures: Both very hot and very cold temperatures can accelerate 12V battery degradation.
• Confusion with High-Voltage Battery: It's important to remember that problems with the 12V battery are distinct from issues with the main high-voltage traction battery.

Regular vehicle software updates often include enhancements to 12V battery monitoring and management, which can help prolong its life.

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