I second the recommendation above. Very pleased with mine, so far.

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Marshall Welch
Seattle, WA
1982 300D-T

Must say the battery must be a few years old .Looking at the top of it .Its the worst battery i have ever seen in my life .I have worked on a lot of cars and never seen one that bad.

What is all over the battery? Did you put something on it, or is it all acid residue? If that is acid, I'd pull the battery tray, and dump baking soda slurry on the paint, and clean it up well... Assuming the fender isn't already corroded away...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

The yellowish stuff on the top of the battery is residual from spraying the terminals with battery cleaner (picture enclosed). BTW, my local car parts place is going to run an exhaustive test on the battery to determine if there are shorted/open cells, etc. Their battery testing machine is a lot better than my simple two buck battery hydrometer. I'll report back with the results of the test.

Is it just me or has the price of batteries gone UP?

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Yup, batteries have become extremely expensive. I recently went to purchase a battery for my W126 which we don't drive much and just about choked when quoted a cost. Decided the W126 looked just fine where it is and whenever I need to drive/move it I can pull out the trusty old battery charger to get it started.

Yeah, yeah, I know, I'm a cheap SOB. My wife lets me know that on a daily basis.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

FYI, your $2 battery hydrometer can do what the expensive battery testing machines cannot do.... specific gravity, which indicates state of charge of each cell. If you fully charged the battery, each cell should show the same full charge specific gravity. It is extremely accurate. What did your $2 tester show? If it showed one cell with low specific gravity, don't waste your time doing further tests, buy a new battery.

I bought an Interstate H8 AGM "take off" from an Interstate warehouse for $40 last summer http://www.interstatebatteries.com/p/mt5-49-h8-audi-a6-2015-33-50-54-55-56-58-v6-3-0l?dsNav=N~21-2147384903 . It's working fine. This "take off" supposedly came from a Mercedes dealer and was taken off a new car and returned to Interstate for whatever reasons. Interstate supplies Mercedes with batteries in the US. Per the manager of the warehouse, all the "take offs" were tested and a percentage of them have nothing wrong with them and sold at their warehouse at a discount. The Mercedes labels were removed and an "Econo Power" label put on before sale.

If you do get an AGM battery, your $2 hydrometer cannot be used since it is a sealed battery (with a pin hole vent).

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The car parts place told me that they had a meter that can determine whether there is a bad cell or not. He put the meter on the battery and ran a series of test. The batter has a bad cell; time to replace! At least I didn't have to sit around for 1 - 2 hours while they ran the more intensive testing.

Ditto, what Funola said about the $2 hydrometer. The parts place discovered what you had already found.

Yes, batteries have gone up. The AGM battery will probably set you back ~$200.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Also, You can test the wires and connections by measuring voltage drop. Take your handy dandy volt meter and put the leads directly onto the posts. Note the voltage. Now move 1 lead to the cable terminal. The voltage should be the same. Now move the 2nd lead to the terminal. Voltage should be the same. Continue moving the lead down the line to the next connection.

You can also measure voltage of individual cells by putting 1 lead in the 1st cell and the 2nd in the 2nd cell. Move the 2nd lead to the 3rd cell then 4th etc. Voltage should increase evenly and be ~1/6 of total voltage.

Professor Google and Duck Duck Go have lots of info.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

OK, bought a new H8 class battery with a three year replacement guarantee! When I use my handy dandy volt meter to test voltage across terminals, I get 12.4 volts. As I move the negative (black) lead to the where the cable attaches via a bolt to the body of the car, I get 12.4 volts when touching the lead to the end of the cable (the eyelet that the bolt goes through to attach to the car body).

HOWEVER, when I place the voltmeter negative lead on the bolt that holds the negative cable to the car body, I get zero or near zero volts. Is this a problem?

I used electronics cleaner on everything before making the connections.

looks like I'm too late to add this...

Napa has 'made in Germany' batteries for w123 for $149. I don't have enough years on them to verify, but they are strong and reliable so far.

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What do you get when you touch the body of the car or the terminal where the bolt connects to the car. Sometimes rusty bolts don't conduct and while you may have a good connection to the body, you can't measure it through a rusty bolt. The same thing happens when your battery post is corroded. You have to scratch to get back to clean metal.

FWIW, the AGM batteries that I looked at were much more expensive than than regular ole lead batteries and had a much shorter warranty. Better still would be to find lead blems for cheap.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Probably not (likely a bad connection between the probe and the bolt), a better test would be a measurement of the voltage between the battery + terminal and the engine (head, intake manifold, block itself).

Does the car start now?

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Yes, that old battery looked absolutely nasty. Although you've already found it had a bad cell and replaced it, I would have recommended removing that battery and giving it a thorough cleaning, especially a baking soda scrub down. Acid contamination of the top of the battery can bleed off some voltage and drain your battery faster than otherwise. A simple test is to measure the voltage between + terminal and various places on the case of the battery, you may be very surprised to see how much voltage is present.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Yes, the car starts and runs fine now. I just checked it with the voltmeter again, placing the positive lead on the positive terminal of the battery and the negative lead on various points on the car. It tests 12.4 volts down to the end of the negative lead.

However, when I place the negative lead on the bolt holding the negative cable to the car, I still get a reading of zero or near zero. I then placed the negative lead on the fender, and get a zero or near zero reading. I did get around 11.5 volts when placing the negative lead on the radiator cap. When I place the negative lead on the valve cover or the thermostat housing, I get 12.4 volts.