Flat battery- W 140

[DoctorGee]

Hello everyone out there.. My battery seems on it's last legs-or so I thought. It's an original MB one.
I don't know how old it was when I got the car last year- but it's becoming difficult to start it. I can't leave the radio on for more than 10 minutes without the engine running, otherwise it will run the battery down. I've had to jump start it twice now. However, before I run off and get a new battery, can someone tell me if it may be a problem with the alternator not charging or some similar other problem?

Thanks,

Greg.

 

[delboy777]

I would doubt it, start the car in the dark leave it to idle for a few moments with your lights on, then give it a rev up and see if your headlights brighten up, if they do, chances are the alt is ok and your battery is knackered. But if your not sure get the batt tested.

 

[television]

The 140 does not have any known battery drain problems, if its only the radio that drains it after 10 mins and nothing else then it does sound like the battery.

If the alternator warning is glowing dimly then that is faulty.
A voltmeter is perfect to see what is happening 12v before start and 13.8 volt with engine running, this would confirm it, they only cost £4 these days.

 

[jibcl500]

Jump starting the car could cause the regulator pack on the alternator to fail, Ive been there and done that to mine. The running voltage needs to be 14.2 volts roughly if its as low as 13.5 ish then I would suggest the regulator pack is failing.
Mercedes is the best place for a new battery the prices are very good, the reg pack can be bought for about £15 off ebay there are several sellers on there for this item.
If your is the S500 then removing the alternator is a fiddle because the anti roll bars below it and some other pipework.
If you need more help pm me.

jib

 

[jibcl500]

Also forgot to mention the CD changer in the boot can be a drain on the battery as once the car been parked up some CD changers will carry on playing each disc even though the radio is off. Make sure the radio is off before you stop the car.

jib

 

[DoctorGee]

Thanks guys- but can you tell me which terminals to check the voltage at?

 

[jibcl500]

Put the multimeter on the battery terminals also have the engine running.

jib

 

[television]

Put the multimeter on the battery terminals also have the engine running.

jib

Check both running where it should be around 13.8 volt, and in the morning where it should be over 12 volt before you start the car and turn the headlamps on when you test

 

[DoctorGee]

Hi Malcolm & Jib,

I just got a multimeter and I've checked the battery. It's 12.2V with the engine off first thing and 14.06 with the engine running and the lights on full beam.. Maybe I'll try leaving the radio on and see how long the battery lasts again.

Greg.