I came out to my 1993 300E today after work (it had sat for about eight hours) and the battery was dead. Completely dead. As in, the car wouldn't turn over, the dome light would barely come on, etc. I was able to get it jumped and get home, and am thinking I might need a new battery.

However, I'm curious about how the battery could completely drain after sitting for that amount of time. I checked various lights, accessories, etc., to see if anything was on/draining power, and found nothing. This also happened once before, but the car had been sitting for a week and I figured it was just because of the time.

Anything particular I should be looking for?

Thanks,
Mike

How old is the battery? Sounds like it's been trounced once before. They do get old and wear out and sometimes, rather suddenly.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

When we bought the car four years ago it came with a new battery, so it's four years old. One of the reasons I'm thinking its best days are behind it.

Any suggestions for what replacement battery to get?

Two choices: #1 Call local MB dealer and see how much they get over the counter for new battery for your car. Could be cheaper than you think, but surely over $100.
#2. Call local Interstate Battery distributor (not dealer) and see what they get over the counter for battery for your car. Dealers sell the same batteries, but charge more since they are in the installation business. I hate to put a non-MB part in my car, but when daughters 300D needed one, Interstate it was. Her car is not exactly a "show car" anyway so I didn't mind having a non-MB battery visible under the hood.
You really should do some testing though to see if something is draining your battery while your car is at rest. Try putting an ammeter in series between the negative cable and battery terminal and see if you have any current draw with car off and doors closed. Anything more than say 50 mA requires looking into. Just pull fuses one at a time till the current draw go away. That should help track down the drain.

Did you know you can bump start many MB autos? The procedure's in the manual.
Saves jump starting, and possibly blowing OVP fuse (grrr)


later

Russ

__________________
190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg

A four-year battery lifespan is not bad these days.

Consider what loads your battery is subject to with all of the engine management systems and electrical accessories modern cars are equipped with.

I think my 300E got 6 years on the OEM unit, but we don't get severe winters in Texas, and the car is garaged otherwise.

Batteries are a wear item, and I'm not a purist when it comes to replacing them. Most forum members here would recommend Interstate products, especially the Optima (a pricey, but indestructible battery).

Truth is, as long as you match or exceed the CCA (cold cranking amps) and group (battery chassis size) and make sure it has the same type of terminals (on top versus side mount) as well as the orientation (+ on left, - on right or vice versa), any brand will do.

I have four cars to maintain...and the Bug takes two batteries, so I'm always looking to save money in this area...

Actually, picked up a couple of batteries for the Bug a month ago for $36 for both!!! Kmart is closing out their stores and had a fire sale!!!

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

I had the same experience - replaced the battery with a new Optima sealed unit thru Interstate. I found that the reason the battery drained down was that the rear passenger dome light was burned out, and the switch was set to 'on'. This circuit also controls the lower courtesy lights in the bottom of the rear doors, which are so dim that I could not see them on with the dark interior, and they drained the battery. So do a current draw test off the new battery when it is installed looking for a draw that could kill the new battery as well! Good Luck.

__________________
John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E

A battery can just go bad internally and be completely dead. Usually happens after a drive of some distance and then sitting for a number of hours. This happened to me in a '97 E320 after 4 1/2 years. Needed battery on weekend so bought the best Die-hard I could get. No problems so far.

I bought a genuine M-B battery at the dealer; cost only $120 (about $20 more than what I was finding at Sears/Interstate). Replacing the old one was a snap, and the car fires up beautifully now. I'm going to do some testing with the ammeter to make sure everything is OK, but it looks like my problem has been solved.

Thanks to everyone for your help. This is such a great resource.

Make sure you get around 13.5 volts at the battery with the engine running at 2000rpm (and all electrical accesories off), then at least 12.5v with the rear defrost on, high beams on, and the heater fan on high.
Otherwise, the new battery could be masking a charging system problem.

Mike,
A simple way to check for excessive key off draw is to go to Radio Shack and buy a 1 ohm 10 watt resistor. Disconnect the negative lead and put the resistor in series. Read across the resistor with a high impedance digital volt meter. If you read a voltage drop of more than .05 volts, you have an excessive key off current drain.

Peter

__________________
Auto Zentral Ltd.

My normally dependable 300E started having some dead battery electrical problems a couple of weeks ago. I replaced the battery, since it lost its charge sitting on the workbench overnight.

After driving the car yesterday, it would not start this afternoon. 10.48 volts. Charged it a bit and got it started. Got the following:

Idle 12.98 - 13.10 v
2000 RPM no load - 13.50 v
2000 everything on - 11.5 v

Tested across the positive post and wire. Could not detect a draw, but this may be due to DMM skills or lack thereof. Poked around and discovered the trunk light bulb was very hot. Pulled the bulb and will see if that solves the problem.

Two questions:

1. Given the readings, should I replace my alternator? Brushes and regulator are about two years old.

2. Where is the trunk light switch?

TIA

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

i had a similar problem on an audi car.
the battery went dead overnight,-it was because the trunk light was on all the the time,which was due to a faulty switch-replaced the switch and problem solved