The 2012 CLS 63 AMG uses a standard 12-volt battery charged through the alternator while driving, or manually with an external charger when the car sits unused

The 2012 Mercedes-Benz CLS 63 AMG does not have a plug-in charging port for the main battery. Instead, the car's alternator charges the battery whenever the engine runs. If the battery drains while the vehicle sits parked — which happens over weeks or months of non-use — you will need an external 12-volt charger to restore it. The battery itself is a standard lead-acid unit located in the engine bay, accessible from the driver's side.

Unlike hybrid or electric vehicles, the CLS 63 AMG has no special charging procedure. The process is straightforward: connect a charger to the battery terminals, set the charger to the correct voltage and amperage, and let it run until the battery reaches full charge. Most owners use a standard automotive battery charger available at auto parts stores or online retailers.

Key Takeaways

  • The 2012 CLS 63 AMG battery charges through the alternator while driving and cannot be charged through a vehicle port.
  • An external 12-volt charger is needed if the battery drains during extended periods of non-use.
  • The battery is located in the engine bay on the driver's side and is accessible without special tools.
  • Charging typically takes 4 to 12 hours depending on the charger's amperage and how deeply the battery has discharged.

Locating and accessing the battery

Open the hood and look toward the driver's side of the engine bay. The battery is a black rectangular box with two cable terminals — one red (positive) and one black (negative). It sits in a plastic battery tray and is held in place by a metal bracket across the top. You do not need to remove any major components to access it; the terminals are when ready visible and reachable.

Before touching the battery, make sure the engine is off and has cooled for at least 15 minutes. Disconnect the negative terminal first by loosening the bolt on the black cable clamp with a wrench, then disconnect the positive terminal the same way. This order prevents electrical arcing. Once both cables are loose, you can lift them away from the battery terminals.

Choosing and connecting an external charger

A standard automotive battery charger rated for 12 volts will work with the CLS 63 AMG. Chargers come in different amperages: 2-amp chargers charge slowly but safely over many hours, while 10-amp or higher chargers work faster but generate more heat. For a deeply discharged battery, a 4-amp to 6-amp charger is a practical middle ground — it will fully charge most batteries in 6 to 10 hours without excessive heat buildup.

Connect the charger's red clamp to the positive battery terminal first, then connect the black clamp to the negative terminal. This order prevents sparks. Plug the charger into a standard wall outlet and turn it on. Most modern chargers have an indicator light or digital display showing charging progress. Leave the charger connected until the battery reaches full charge, which the charger will signal either by a light change or an automatic shutoff.

Charging time and what to expect

A completely dead battery typically takes 4 to 12 hours to charge fully, depending on the charger's amperage and the battery's condition. A 2-amp charger may take 12 hours or more; a 10-amp charger may finish in 4 to 6 hours. If the battery is only partially discharged — the car cranks slowly but still starts — charging time will be shorter.

During charging, the battery may warm slightly, which is normal. If the charger becomes hot to the touch or the battery itself feels very warm, turn off the charger and let everything cool for 30 minutes before resuming. This prevents damage to the battery's internal cells. Once charging is complete, disconnect the charger by removing the black clamp first, then the red clamp.

Reconnecting the battery and starting the car

After the battery is fully charged, reconnect the cables in reverse order: red clamp to the positive terminal first, then black clamp to the negative terminal. Tighten both bolts firmly with a wrench so the clamps do not slip during engine operation. Loose connections can cause starting problems or electrical faults.

Start the engine and let it idle for 2 to 3 minutes. The alternator will begin charging the battery when ready. If the car starts normally and all dashboard lights function, the battery is ready for use. If the engine cranks slowly or does not start, the battery may need additional charging time or may be defective and require replacement.

Preventing battery drain during storage

If you plan to park the CLS 63 AMG for more than two weeks without driving it, consider using a battery maintainer — a low-amperage charger designed to stay connected indefinitely. A maintainer supplies just enough current to offset the battery's natural self-discharge rate, keeping the battery at full charge without overcharging. These devices cost between $30 and $100 and connect the same way as a standard charger.

Alternatively, disconnect the negative battery terminal if the car will sit unused for a month or longer. This stops all parasitic drain from the vehicle's electronics. When you are ready to use the car again, reconnect the terminal and charge the battery if needed. Always reconnect the negative terminal last to prevent accidental arcing.

When to replace the battery instead of charging it

If the battery will not hold a charge after a full charging cycle, or if it repeatedly drains within days of being charged, the battery is likely defective and needs replacement. A battery that is more than 3 to 5 years old may also fail to charge properly even if it appears functional. Most auto parts stores can test a battery for free to confirm whether it is still good.

The 2012 CLS 63 AMG uses a battery with a specific size and terminal configuration. When replacing it, purchase a battery rated for this model year — typically a Group 47 or Group 48 battery with 600 to 700 cold-cranking amps. Installation is the same as reconnection: disconnect the negative terminal first, remove the old battery, install the new one, and reconnect both terminals with the negative last.

Frequently Asked Questions

Can I charge the battery while it is still in the car?

Yes. You do not need to remove the battery to charge it. straightforward open the hood, connect the charger clamps to the battery terminals, and plug in the charger. Make sure the engine is off and the charger is unplugged before you disconnect the clamps.

How do I know if the battery is fully charged?

Most modern chargers have an indicator light that turns green or a digital display that shows "full" or "100%" when charging is complete. Some chargers automatically shut off when the battery reaches full charge. If your charger has neither feature, check the battery voltage with a multimeter — a fully charged 12-volt battery reads between 12.6 and 12.8 volts.

What happens if I connect the charger clamps backward?

Connecting the clamps in reverse (black to positive, red to negative) will not charge the battery and may damage the charger or blow an internal fuse. Always connect red to positive first and black to negative second. If you realize you have connected them backward before turning on the charger, disconnect and reconnect them correctly.

Is it safe to drive the car when ready after charging?

Yes, the car is safe to drive as soon as the battery is fully charged and the cables are reconnected. The alternator will take over charging as soon as the engine starts. However, if the battery was completely dead, let the engine idle for a few minutes before driving to may support all electrical systems are functioning normally.

Do I need any special tools to charge the battery?

No special tools are required beyond a standard wrench to loosen and tighten the battery cable clamps. A multimeter is helpful for checking battery voltage but not necessary. The charger itself comes with clamps that attach directly to the battery terminals without additional equipment.