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Semi-OT battery question

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Initially Posted - 06/15/2012 : 23:03:39

I'm pretty sure the battery in my Mercedes is toast. It'll take enough of a charge that I can start the car once or twice. But then the battery is dead again. I think it's charging properly, but I haven't done any real testing other than making sure the voltage increases to the right-ish level when I accelerate the engine. I drove it to the marina today with no problems (a 2-1/2 hour drive instead of the normal 40 minutes). However when I went to start it to go home about four hours later, it tried to turn over once, then nothing. Great. I'd had the foresight to bring along a jumpstart battery with me, and was able to immediately get the engine started with that. I had no problems driving home and my lights seemed to be OK the whole time. As soon as I stopped the car, I tried to start it again, and nothing, just a brrrr and dimmed dash lights. I've got it on the charger right now and it should come up to "full" charge in a few hours.

I'll probably take it to Sears tomorrow and have them check the system for me.

What I know about batteries, I learned more than 30 years ago in the USN, so if anyone has any suggestions, I'm all ears.

David
C-250 Mainsheet Editor

Sirius Lepak
1997 C-250 WK TR #271 --Seattle area Port Captain --

Edited by - on

Sloop Smitten
Master Marine Consultant

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USA
1181 Posts

Response Posted - 06/16/2012 : 02:04:24

The fact that you can jump start it and it will run is a pretty good indicator your charging system is working. It could be bad battery cables or connections but I think your battery is toast.

Edited by - Sloop Smitten on 06/16/2012 09:22:46

TCurran
Admiral

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USA
588 Posts

Response Posted - 06/16/2012 : 05:21:49

what Joe says.

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Joe Diver
Master Marine Consultant

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USA
1218 Posts

Response Posted - 06/16/2012 : 05:28:47

Battery is gone.

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Stinkpotter
Master Marine Consultant

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Djibouti
9089 Posts

Response Posted - 06/16/2012 : 07:31:32

I think the Sears guy is going to laugh...

Be careful with sparks--that piece of toast could be generating copious amounts of hydrogen gas. An exploding box of sulfuric acid is not something you want to be around.

Edited by - on

pastmember
Master Marine Consultant

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2402 Posts

Response Posted - 06/16/2012 : 07:33:00

The replacement for my BMW was odd, large, and required battery back up to the car during exchange. I ended up with an Autocraft from Advance Auto. Most batteries are made by just a couple manufacturers. Point is you should find a good replacement without going to the dealership.

Edited by - pastmember on 06/16/2012 07:45:19

Stinkpotter
Master Marine Consultant

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Djibouti
9089 Posts

Response Posted - 06/16/2012 : 07:35:39

Frank--what's the point of that huge photo, other than making the thread unintelligible? (Let's see if you can find the box to reply in.)

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pastmember
Master Marine Consultant

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2402 Posts

Response Posted - 06/16/2012 : 07:46:58

Silly boy, I am not evil, just learning how a new hosting service works. The "view at original size" option seems to be a mistake, this one is simply the "large" size. His battery size may be the same odd size as mine which has a Euro number and a USA number, my photo shows the USA number.

Edited by - pastmember on 06/16/2012 07:50:03

pastmember
Master Marine Consultant

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2402 Posts

Response Posted - 06/16/2012 : 07:47:39

But that was a big honker, huh?

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Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 06/16/2012 : 10:10:29

I would suggest that you check for a parasitic drain before you replace the battery.

I agree that you will end up replacing the battery here, but you may find that there is a ground or something that is draining the battery down. You should be able to check this by disconnecting the negative terminal, and putting a multi meter between teh terminal (now disconnected) and teh battery lead. If you get a reading on the meter, something is drawing down the battery.

Assuming you get a reading, have Rita pull the fuses in the fuse block one at a time, replacing them after she pulls them while you watch the multimeter. Whichever fuse brings the reading down has something pulling juice off the battery on its circuit. You should have a little draw on the radio (memory for presets), and maybe the security system, but everything else should be dead.

Another possibility is that a bad alternator or starter can kill a battery as fast as you can say Jimminy Christmas. I hate when I get caught in this loop, and inevitably end up replacing all three items at the same time. A real garage will only replace the item that needs replacing, but for the labour costs nowadays, I can do all three in my driveway for what they would charge for any one. I refuse to pay a garage to replace a battery or alternator in a "standard" layout anyways (Battery and Alt up top and in plain view). I may pay for a starter to be replaced if I don't feel like crawling under the car. YMMV

Edited by - Prospector on 06/16/2012 10:12:57

Stinkpotter
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Djibouti
9089 Posts

Response Posted - 06/16/2012 : 10:34:14

Much better, Frank...

Good point about the draw on the battery--I had a real mystery of that type on a '71 Chevy--replaced a battery only to have the new one quickly go down. Nobody could find a draw, until once when the meter was on and somebody noticed when it suddenly spiked, and then dropped back down after a while. Turned out to be a solenoid on the A/C compressor, periodically trying to turn the compressor on and off (even though the car was switched off). There's no end of possibilities... But that instance when you drove for a while, stopped, and <i>immediately</i> tried to start again--there should have been enough there to crank if the battery was "normal". If there was a hard enough short to cause that, it should have blown a fuse long ago.

Edited by - Stinkpotter on 06/16/2012 10:35:00

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 06/16/2012 : 10:54:30

Dave - I have heard similar stories about cooling fans (the one in front of the rad, not the squirrel cage fan for climate control) continually cycling although the car has been sitting.

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 06/16/2012 : 12:43:03

Thanks for the advice guys. The battery is a Diehard group 49. There's no way I'd even consider taking this to the dealer. The car is nearing 40 years old ('76 diesel). The battery is probably more than five years old and we've had similar problems in the past. The idea of the parasitic load is a good one. I very recently replaced the series glow plugs with parallel glow plugs, but continued to use the original glow plug relay, which seems to work fine. However, I suspect the relay is engaging after the light goes out, I can occasionally hear something under the dash clicking while I'm driving. My original suspicion with regards to the glow plug system was the relay, but after following instructions on a Mercedes forum, the parallel system seems to be working very well (car starts right up instead of having to wait forever for the glow light to go out). If the relay is the problem, I may simply replace it with a Ford type solenoid with a momentary contact switch for the glow. That way I know the circuit is dead once you take your finger off the glow switch.

I'm going to read up a bit more on how to test the charging circuit myself.

The nice part is since this car is so old, it's pretty easy to work on. The battery is right up front and exposed.

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 06/16/2012 : 13:40:05

David,

If the car is running, nothing should be able to outpace the charge going into the battery. usually what kills a battery is something that is drawing it down with the car off. I can't think of a time I have had a car drain the battery while driving - except when an alternator let loose.

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SEAN
Admiral

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USA
772 Posts

Response Posted - 06/18/2012 : 05:10:14

from what i know , it sounds like a regulator or alternator ..

your car should be charging the battery while running ..
check the battery with a voltmeter off , then again running , it should be go higher in the 13s running

you only need the battery to start the car , then the alternator charges again for the next start

Edited by - SEAN on 06/18/2012 05:13:38

Stinkpotter
Master Marine Consultant

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Djibouti
9089 Posts

Response Posted - 06/18/2012 : 19:49:08

Unless it's a "maintenance free battery" which, when it goes, is GONE and won't accept a charge. I repeat--this could be an unsafe situation. Don't mess too much with it yourself.

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OLarryR
Master Marine Consultant

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USA
3478 Posts

Response Posted - 06/19/2012 : 03:35:14

Ditto what everyone has said.

Generally, when a battery is 5+ years old, that is usually when they lose their life and a replacement is needed. When the battery is newer than that percentages increase that it is some other deficiency. Sometimes, it is a combo of deficiencies that contribute to poor performance and that then makes the diagnosis harder. The usual suspects with most likely cause depending on age of battery is a dead battery, loose/poor cable terminal contact, alternator weak, battery drain from somewhere in the circuit or the voltage regulator is faulty. At some time or another one or all of these deficiencies has probably been experienced by all out there. I have had each one at some time or another. I recall one car where the battery prematurely went dead but took a full charge and then went dead a few days later again. Diagnosis turned out to be the little light in the trunk which stayed on with the trunk closed !! So...you never know about these things.

The easiest thing to do before going out and getting a new battery or a diagnosis from a shop is to take the terminals off and sand the insides of the terminals that connect to the battery. However, as these cars get more and more electronically dependent, disconnecting the terminals may goof up some of the electronics that must be connected all the time. Your owners manual may indicate if that is the case. If cleaning of the terminals does not solve the issue and given it is over 5 years old, then most likely a battery replacement will resolve the issue. If it was a newer battery...then I probably would take the car in for an electrical diagnosis to rule out one of the other potential deficiencies. However, some shops, maybe most, will provide a free diagnosis and battery install when buying a battery and so bringing the car in may be the best route to be done with it.

Edited by - OLarryR on 06/19/2012 03:39:19

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 08/07/2012 : 19:30:22

Just thought I'd give an update to this.

A few weeks back Rita & I were pretty close to a Walmart Supercenter, so we stopped in to see if I could find a battery for the Mercedes. As luck would have it, the car parts store was "closed", all the lights were off in it, but you could still go inside. So I poked around for the size battery I was looking for, but only saw one that seemed like it would fit. However, it wasn't the right size on the label. Hmmm...Decided to look in the little catalog hanging on the rack, and the battery I'd see indeed was the right one, they just used a proprietary code for it. There were two of them in the rack, and one in the back had a more recent manufacture's date, so I grabbed it. Installed it the next day, and no troubles starting the car.

We didn't trust it for a few weeks, worried that the new battery might get drawn down, but that was weeks ago and we've never had a problem, so it looks like it's solved.

Thanks to everyone for their input, I really appreciate all the help!

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