Introduction

There are many systems in your car that depend on a well-performing battery. Since modern batteries are sealed they are fairly low maintenance items. However, they should not be completely ignored. Learn to keep yours performing well.

The battery on diesel W123 cars is located in the far rear left corner of the engine bay, as you face it from the front of the car.
  • The battery on diesel W123 cars is located in the far rear left corner of the engine bay, as you face it from the front of the car.

  • This battery is in fairly good shape, but has not been maintained in several years and has gotten dirty and could use some love...

  • To begin, disconnect the positive and negative battery terminals. This will be covered further in Step 3.

  • Be aware that batteries contain corrosive materials, release potentially explosive gasses, and can output a painful and potentially dangerous 12v shock. Use common sense, keep away from open flames, don't use strong chemicals around the battery, wear gloves and safety glasses etc.

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Make note of which terminal is which. On many new cars, the positive terminal is marked with red while the negative is black.
  • Make note of which terminal is which. On many new cars, the positive terminal is marked with red while the negative is black.

  • On a W123 however you may need to depend on the small "+" sign to find the positive terminal.

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Use a crescent wrench to loosen the nuts on the battery terminals. Do not remove the nut fully, just loosen it enough to remove the terminal. On W123's, this nut is likely a 13mm. Pull the terminals off, starting with the Negative "-" terminal, then the Positive "+" terminal.
  • Use a crescent wrench to loosen the nuts on the battery terminals. Do not remove the nut fully, just loosen it enough to remove the terminal. On W123's, this nut is likely a 13mm.

  • Pull the terminals off, starting with the Negative "-" terminal, then the Positive "+" terminal.

  • Never remove the positive terminal first, or you risk injury from electric shock.

Every manual I have ever read says remove negative first.

Thomas Docherty - Reply

Use a soft metal brush, like the brass brush shown, to clean any corrosion off of the inside of the terminal. Follow this up with a spray of electric contact cleaner.
  • Use a soft metal brush, like the brass brush shown, to clean any corrosion off of the inside of the terminal. Follow this up with a spray of electric contact cleaner.

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Use a soft metal brush to clean any corrosion or dirt from the battery posts.
  • Use a soft metal brush to clean any corrosion or dirt from the battery posts.

  • Then use some mild cleaner on a damp shop towel to wipe down the rest of the battery of dirt and corrosion.

  • If your battery is really dirty, and has lots of corrosion, consider purchasing a spray can of battery cleaner designed for heavier cleaning.

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Reconnect the terminals to their appropriate posts and enjoy the fresh clean battery!
  • Reconnect the terminals to their appropriate posts and enjoy the fresh clean battery!

  • Optional but recommended - cover the battery terminals with a light coat of dielectric silicone grease after tightening them in place. This will help prevent future corrosion.

  • Do not put dielectric grease between the terminals and the posts, only on the outside of the terminals. Any grease between the posts and terminals will add resistance to the flow of electricity as dielectric grease does not conduct electricity by design.

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Conclusion

To reassemble your device, follow these instructions in reverse order.

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Nicolas Siemsen

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2 Comments

It might be helpful to add that the negative battery terminal should be removed first, and isolated. Disconnecting the positive terminal first could lead to a short (and sparks) if the wrench contacts another metal object. There is an old story of a left handed man who disconnected the positive first and the wrench touched his wedding ring. In short, he practically arc welded the wrench to his ring and burnt his finger badly.

Jeff - Reply

Hi. Can the gas battery be maintained or the distilled water is increased or changed. And how so if the answer is yes

abdoo erajhi - Reply

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