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1985 380sl - charcoal grey w/lt grey interior
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182 Posts
Discussion Starter #1
all,

trying to determine if my battery needs replacing...i don't use my car much and a couple of weeks ago i had a voltage reading of 10.50 and my car would not start...i jump started it and the alternator brought the voltage up to 12.89 after idling for 5 minutes and after shutting off it stayed there for a day or so and then starts to drain.

with car not started, today i tested the DRAW on the battery and it is reading 7.34 amps

my vw passat reads 4.35 amps and my isuzu trooper reads 4.95 amps when not started.

is this 7.35 reading any indication that i have too much draw on the battery??
 

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Registered
Dallas, Texas
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7,700 Posts
Time to do some reading. Some general info on car batteries is here.
Automotive battery - Wikipedia, the free encyclopedia

Then open your meter manual and find out how to set it to proper scale. 7.34A is 88 Watts. You should see something glowing real bright. 55W headlight bulb draws only 4.6A.
 

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Premium Member
'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,327 Posts
all,

trying to determine if my battery needs replacing...i don't use my car much and a couple of weeks ago i had a voltage reading of 10.50 and my car would not start...i jump started it and the alternator brought the voltage up to 12.89 after idling for 5 minutes and after shutting off it stayed there for a day or so and then starts to drain.

with car not started, today i tested the DRAW on the battery and it is reading 7.34 amps

my vw passat reads 4.35 amps and my isuzu trooper reads 4.95 amps when not started.

is this 7.35 reading any indication that i have too much draw on the battery??
How did you measure the draw? Draw couldn't be that much. Possibly mA? Relative to those other cars, it is quite likely the MB would be higher.

I have measured mine, and used two methods. One was a clamp on meter around the positive cable. The other was a regular digital voltmeter connected between the battery positive and the disconnected battery positive cable.

The clamp on told me something, but the DVM, not much. Problem is that each time I connected the meter various things start up in the car's systems. The ECU, a fan in the upper console etc. Even opening a door will trigger these things, so the clamp on meter reading was also suspect.

Best thing is to disconnect battery and fully charge it with a proper battery charger. Then use a load tester as pictured above to test the battery. If you don't have one, places like Autozone and anyone selling batteries should test it for you at no cost.

If the battery tests out good but still runs down, you may have a current leak somewhere. Lots on the forum about possibilities like seat adjusters, alternator etc. But these cars do run down in 3 or 4 weeks on their own. If car is not used for long periods, a smart battery maintainer like the C-Tek one should be left connected.
 

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Premium Member
2001 E320 - Brilliant Silver/Ash: 107,000+
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17,193 Posts
Also free at almost any battery store. We have an Interstate store that I have used for another car. I don't know if they make the right one for my MB.
 

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'02 E320 4matic Wagon
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326 Posts
Cant be that much amperage when it is just sitting, unless you have the CAN network awake and something like the radio on. Let us know how you are measuring.

all,

trying to determine if my battery needs replacing...i don't use my car much and a couple of weeks ago i had a voltage reading of 10.50 and my car would not start...i jump started it and the alternator brought the voltage up to 12.89 after idling for 5 minutes and after shutting off it stayed there for a day or so and then starts to drain.

with car not started, today i tested the DRAW on the battery and it is reading 7.34 amps

my vw passat reads 4.35 amps and my isuzu trooper reads 4.95 amps when not started.

is this 7.35 reading any indication that i have too much draw on the battery??
 

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W210 Moderator
99 E320
Joined
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5,105 Posts
pt- don't we still need to swap mirror for cash or something? i'm not an expert
electrician or anything but i can tell when a needle is deflecting. i can help you
perform preliminary diagnostics on your battery for starters.

this week i'm available FRI, and early SAT. or, the following weekend. r-
 

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Registered
1985 380sl - charcoal grey w/lt grey interior
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182 Posts
Discussion Starter #9
raymond...i will pm you my phone #
 

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Registered
1985 380sl - charcoal grey w/lt grey interior
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182 Posts
Discussion Starter #10
sorry for the inaccurate info...the reading was in fact mA (milli amps) not amps.
 
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