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Battery

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Definition

The car's battery is a source of stored electrical energy.

Original equipment batteries measure 260mm x 180mm x 222mm (LxWxH). Equivalent US dimensions are approximately 10-1/4" x 6-7/8" x 8-3/4" (LxWxH).

Compared to BCI standards, the positive and negative terminals are reversed and this needs to be taken into consideration when selecting a replacement battery. Fortunately, "reversed" batteries are readily available so this is not a problem as long as you get the right setup.

In particular, the battery terminal orientation is show in the following diagram:

Front of car

+-----------+
|           |
|           |
| --     ++ |
+-----------+

Rear of car

The following chart lists a number of possible replacement batteries. Note that all heights include the battery posts.

BatteryLxWxH (mm)LxWxH (in)Notes
Orignal260 x 180 x 22210-1/4 x 6-13/16 x 8-3/4Varta/MB pn 003 541 33 01
BCI 24F273 x 173 x 22910-3/4 x 6-13/16 x 9Longer and taller than original size
BCI 24R260 x 173 x 22910-1/4 x 6-13/16 x 9Taller than original size
BCI 34R260 x 173 x 20010-1/4 x 6-13/16 x 7-7/8Closest match to original size

Note that the "R" and "F" designations indicate reversed battery poles as required by our cars.

Note that the cable connectors to the battery posts cannot be switched. That is, the negative ground cable will not fit onto the positive post because of different diameters:

Function

The battery is an electro-chemical device that stores electrical energy to power accessories while the engine is shut off, and most importantly to start the engine. The battery is recharged by the alternator while the engine is running.

All car batteries are the lead-acid type (basis for the chemical reaction). There are three basic types of lead-acid batteries: flooded, AGM, and Gel. Flooded batteries are most common and use a liquid electrolyte. Some flooded batteries have removable caps to check the electrolyte level and replenish with distilled water. So-called "Maintenance-free" batteries are also flooded batteries, but the caps are not removable, or are more difficult to remove. Although not intended, the electrolyte level can often be checked and topped up.

AGM stands for Absorption Glass Matt and is a form of truly sealed battery. Rather than freely sloshing around, the electrolyte is absorbed into a sponge-like material inside the battery. AGM batteries require no maintenance, and cannot be maintained even if you wanted to. This is both good and bad. No maintenance is good, but if AGMs are overcharged they can lose electrolyte which cannot be replaced.

Gel cells are also sealed, but rather than suspending the electrolyte in a sponge material, the electrolyte itself is of a gel consistency. Gel cells have the same maintenance characteristics (pro and con) as AGMs.

Maintenance

Lead acid batteries need to be kept fully charged, and need to have their electrolyte level maintained.

Any car that is run on a regular basis will encounter enough engine run time to maintain a fully charged battery. Cars that sit around a lot are another issue. Batteries themselves have a self-discharge rate, plus the clock and perhaps other accessories continuously draw small amounts of power. The combined result is a slow discharge on the battery. You might think this is fine as long as their is enough remaining charge to restart your car, however it's more complicated that that.

As a battery discharged, lead sulfate forms on the plates as part for the normal chemical reaction. Recharging reverses the reaction and removes the sulfate. The problem occurs when the sulfate is left sitting around too long. Over time it hardens and makes the reverse chemical process more and more difficult. As more and more hardened sulfate is left behind, the battery loses capacity and eventually is no longer serviceable.

For those of us who park our cars for the winter, or otherwise leave it standing for extended periods, a periodic recharge will help extend battery life. Fully recharging once a month is a good rule of thumb. Leaving a battery maintainer connected is another option, but consider safety and fire risk is you do this.

For batteries where the cell caps can be removed, check the electrolyte level once a year. If it's low, top up with distilled water. Tap water is often fine, but the problem is you have no idea what's in it. Using distilled water is a simple, inexpensive way to be sure you are not introducing contaminates. Please note that you should never top up with battery acid. The acid itself does not evaporate. The chemical reaction cracks water atoms into hydrogen and oxygen and the two gasses escape. That's why all you need to replenish is water. AGM and Gel batteries chemically recombine the oxygen and hydrogen internal to the battery. However, if you overcharge and AGM or Gel the gasses are produced faster than they can be recombined and the excess is vented with no means of replenishment. As you can imagine, chronic over charging will quickly kill an AGM or Gel.

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I was wondering if any of the original owners remembers the type, color, size, style of the original batteries that came with the car. Were they Varta? Black? 55AH (Amp x hours) ?

Hans Strom: The tar-top batteries (in Europe) had the measurements: length 260mm, width 180mm, height 200mm. 55 Ah is fine. I donīt know if US vehicles had a different type (size) installed.

Driving down the road yesterday, stopped at a traffic light, and turned the car off to unlock the glovebox. Tried to turn it back on and found battery dead. I'm thinking alternator. Also, the car was running a little hot before that--still thinking alternator/not enough power to turn the fan in traffic. Does this sound plausible? How hard is it to get alternators/any ideas on what to get (stock or another type/brand)?

Did you replace the battery within the last 5 years? If not then it's likely the life span of the battery is exhausted. Charge the battery overnight with a charger and check the status, if good then the regulator on the alternator is bad or alternator itself is bad. As for the heat? That is a seperate matter, could be a number of things.

Will: How about a loose fan belt not driving the alternator or the waterpump fully?

About six months ago I noticed the battery was bubbling over, so I replaced it with a new one. Now I see the new battery is doing the same thing. Could this be an alternator problem? How do I check it?

Voltage regulator

What battery (and what size) should I get for the car? Are points deducted for using a Sears Die-Hard?

According to Sears, the battery group size is 35 (9 1/16" x 6 7/8" x 8 7/8"). Their Die-Hard costs about half the wholesale price for a battery from Mercedes. I believe that using a Die-Hard probably will cost points in a concours competition.

Some members have discussed having old battery cases rebuilt to keep the original appearance so I'm sure a Die-Hard would not past muster. Pete Lesler or Tom Hanson could answer for sure. I'm surprised at the price difference. I just bought a battery from the local Mercedes store (p/n 003-541-33-01) for $126.78 Canadian, including a 10% discount for MBCA membership. That's about US$83 - is a Diehard that cheap?

Albert: do you have the original frame-support for the battery ? Because this black square frame on top of the battery gives you the max. size of the battery. I have a Bosch Silver (55 Ah) on my car, and it fits well.

I've ordered the battery frame, but it hasn't arrived yet. What are the dimensions of your battery? According to Ray Paul at Star Quality parts, the dimensions should be 10" long, 6 7/8" wide on top, and no more than 7 3/4" tall (approximately 25.4cm x 17.5cm x 19.7cm). The Mercedes part number is 003-541-3301. It's expensive, but I'm having some trouble finding a non-Mercedes battery short enough.

You got a great price!! The best price I've found on a Mercedes battery is about $120, whereas a Die-Hard (6 year warranty) costs about $67 here. Apparently Sears was wrong about the battery group size. According to Ray Paul at Star Quality, the dimensions (L x W x H)) should be 10" x 6.875" x 7.75", or approximately 25.4cm x 17.5cm x 19.7cm). Those should match the dimensions of your battery. I'm having trouble finding a non-Mercedes battery short enough. For batteries, the original equipment is expendable, and "can be replaced with a battery of any OEM if it is of the like dimension and form as the original". That seems to say it must come from Mercedes. The rule for tires is looser - they "can be replaced with comparable or superior equipment of original size or MBCA allowed replacement size and compatibility with the vehicle".

Dimensions of my Bosch Silver (5D) are: Long: 24,5 cm, Wide on top: 17,5 cm, Tall: 18,5 cm (but there's enough place up to 21,5 cm). Inner dimensions of top frame support: Long: 27,0 cm, Wide on top: 17,5 cm. So you can install a battery with max. size of 27cm x 17,5cm x 21,5 cm. When you order your battery, remember to indicate which side is the positive terminal (right side). Note: Hoppecke was also a factory equip battery.
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