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What to look for in buying a new battery:
What do I honestly think is the best way to buy a battery? Call 1-800-FOR-MERCEDES and tell them you need a battery. They'll send a guy in a truck, who will remove your old battery, install the "correct" new battery, synchronize all your electronics, and haul away the old one - all for the retail price of the battery. That's right, no delivery fee, no installation fee, nothing other than the price of the battery. That's for any Mercedes-Benz. They don't care if the car is 4 years old or 40 years old. They also don't care if you're the original owner, what day it is, or what time it is. If your battery dies and you don't want to buy one Mercedes-Benz roadside assistance will properly jump-start your car, bring you a few gallons of fuel, or change a flat tire using your spare, all free of charge. If every manufacturer was like Mercedes-Benz, companies that sell roadside assistance insurance would be out of business.
If you decide to buy a battery and install it, get a good one. Don't go cheap and find yourself stuck in minus 20 degree weather, or on the side of the road when it's 115 in the shade. How do you tell whether a battery is any good? The most important features to look for will be dependant on where you live. If you live someplace cold, it will be cold cranking amps. If you live somewhere hot, it will be reserve capacity.
Cold Cranking Amps are commonly listed as a battery's CCA rating. Cold cranking amps are the discharge load, measured in amps, that a fully charged battery at 0 degrees F can deliver for 30 seconds, while maintaining a voltage above 7.2 volts. Every car has a cold cranking amperage requirement. That requirement can easily be seen by looking at the sticker on the original equipment battery in your car. The battery will have the word "Kaltstarstrom" followed by a number The literal translation for Kaltstarstrom is "cold start current". Based on the tag on my battery, mine has 450 CCA. If you no longer have the original equipment battery, you can ask your dealer's parts department. In colder climates, the higher the cold cranking amperage rating, the lower your chances of getting stuck someplace and freezing to death.
In hot climates, buying batteries with double or triple the original cold cranking amperage rating is a waste of money. That's because in hot climates, reserve capacity is king. Reserve capacity is frequently referred to as RC. Reserve capacity is the number of minutes a fully charged battery at 80 degrees F can be discharged at 25 amps until the voltage falls below 10.5 volts. More RC is better, even in cold weather. For example, if your car has a 360 cold cranking amp requirement, then a battery with a 450 cold cranking amp rating with a 120 minute reserve capacity is much better than one with 850 cold cranking amps and only a 90 minute reserve capacity. Why do you need reserve capacity? Because something has to power your clock, alarm, courtesy lights, delayed headlamps, radio, and all those other electrical gizmos that require power after the car is turned off.
So what else is important?
- A fresh battery would be nice. Fresh as in, one that hasn't been sitting on the shelf for the past two years. I've seen the battery rack at my local Mercedes-Benz dealer. They always load from the back and pull from the front. That ensures they rotate through their stock. The Mercedes-Benz roadside assistance truck gets their batteries from dealers. They pulls those batteries from the front as well.
- How about a battery that fits in the hole the original battery came out of? I don't know about your battery, but the one in my Mercedes-Benz is HUGE. The replacement shouldn't require some special strap to hold it in place, or a block of wood to make up for the excess room. On the other hand, it shouldn't be some oversized bus battery because that's the closest thing they had in stock. Think of a battery as you would a pair of shoes. You wouldn't buy some oversized clown shoes or leave the store wearing something that's four sizes too small. It should "fit".
- The original battery in a Mercedes-Benz has a vent tube. Your new battery should have a vent tube. Don't listen to someone who says, "It'll be OK without one." If it was OK, Mercedes-Benz wouldn't have spent the money to install vent tubes in every car they make.
- Lastly, this is just a battery. It shouldn't cost four zillion dollars. Some people see you drive up in a Mercedes-Benz and think you're supposed to pay extra. Right about now some people may say, didn't you just recommend paying retail for a "Mercedes-Benz" battery? Consider this - Interstate is a large battery manufacturer. They advertise that they are the "#1 replacement battery brand in the United States". List price on an Interstate MTP-93 battery, which is what Interstate claims is the correct battery for my car, is $138.95. The battery I bought from Mercedes-Benz has a retail price of $118. That's before my Mercedes Benz Club of America discount. So for $20 less, someone will deliver and install a new battery, and if you're a member of the Mercedes Benz Club of America, you get a discount on top of that. Did I mention that the Mercedes-Benz battery is the correct one?
If you absolutely, positively insist on changing the battery yourself, here's one way to do it without having to reload the security code in the radio, re-sync the express windows, reset the memory in your seats, reset the sunroof, and clear the ESP error - a charger can be connected to the hot wire under the hood before disconnecting the battery in the trunk. After the new battery is hooked up, disconnect the battery charger. The car never actually lost power, so there was nothing to reset.
The red arrow points to a cover. On a CLK, there is a hot wire underneath where one could make the positive connection. The positive wire is in different places on different models. The negative can be hooked to just about anywhere else.
If for some reason the power supply is interrupted (battery disconnected) the windows, seats, BAS/ESP, and sunroof can be re-synched as follows:
- Press the power window "up switch" until the window is completely closed, and hold it for additional 2 seconds. Repeat this procedure for each window.
- Put the key in the steering lock, and turn it to position 2. Move the seat completely forward and the head rest fully down, and hold both buttons for approximately 2 seconds. Do this for both seats
- Start the car. Turn steering wheel completely to the left and then to the right. This will clear the electronic stability program error.
- Put the key in the steering lock, and turn it to position 2. With the sunroof closed, push the sunroof switch up until the sunroof is completely raised at rear, and hold the switch for additional second.
The clock and radio will have to be reset as well.