Disconnecting battery sets off an alarm

[eyelight]

We haven't driven our 1994 E220 in a while, and consequently the battery is flat. Borrowed a charger from a neighbour and started to take battery out of caar to charge it, but as 3 seconds after taking off the positive lead an alarm started. So even though I currently have the main car alarm turned off, the car obviously has a secondary system which we've never known about.

Sounds like it's coming from the front of the engine somewhere, but can't really trace it.

Has anyone encountered this before or has anyone got ideas on how to bypass or shut off this battery alarm?

Thanks,
Larry

1994 E220 Coupe
1994 E280 Estate

 

[bigasotonuk]

Hi,
This is quite normal as the alarm has a battery back-up in the siren.
Is your battery so flat that you can,t turn your alarm off normally? then remove the battery.
You could always charge the battery with it still connected, i,ve done this to my my 230k.

 

[eyelight]

Thanks, I'll try and have another look at it later today.
Makes sense that there'd be a backup system, though my only other car with an alarm, 1990 BMW 525i, and nothing like that. Removed and replaced battery several times from that one with no drama.
Car parked on street around the corner from house so will have to remove battery to charge.

 

[wireman]

When you disconnect a cars battery take the un earthed (-ve) side off first, then if your spanner shorts to earth/body it will not turn into a hand held electric fire. Re connect the earthy side last.
Same goes for jump leads.

 

[Schtum]

Thanks, I'll try and have another look at it later today.
Makes sense that there'd be a backup system, though my only other car with an alarm, 1990 BMW 525i, and nothing like that. Removed and replaced battery several times from that one with no drama.
Car parked on street around the corner from house so will have to remove battery to charge.

Good luck with that. (See my post on breakdown)

BTW. I would never charge a battery on the car. Too risky by half IMHO.

 

[JEZ.S320L]

Hi,
This is quite normal as the alarm has a battery back-up in the siren.
Is your battery so flat that you can,t turn your alarm off normally? then remove the battery.
You could always charge the battery with it still connected, i,ve done this to my my 230k.

Does this apply to ALL MB's with factory-fit alarms?

 

[bigasotonuk]

Hi,
I 'think' this applies to all the more modern vehicles, or any that have a factory fitted 'Thatcham' approved system like my C230K.

 

[JEZ.S320L]

In Summary:

It is not recommended to:

a) Change the battery
b) Mess with electrics
c) Dabble with anything that requires i) spanners ii) wrenches iii) socket sets iv) screwdrivers v) pliers
d) Do anything that requires you to wash your hands afterwards

Sounds good to me..!!

Press button - open door - start engine - drive - switch egine off - open/close door - press button.

THAT's how a car should be...

 

[eyelight]

When you disconnect a cars battery take the un earthed (-ve) side off first, then if your spanner shorts to earth/body it will not turn into a hand held electric fire. Re connect the earthy side last.
Same goes for jump leads.

Thanks Wireman. I knew this, and have always done it in that right order but somehow didn't do it that way yesterday.

Doing a google search for battery disconnecting and alarm brings up other make forums (notably Vauxhall) where the advice is to disconnect the battery while the key is in the ignition and turned to position 2, or to turn key to position 2 and take out, and quickly disconnect battery in 15 seconds.
Anyone tried that with a mid 90's Mercedes ?

 

[JEZ.S320L]

Thanks Wireman. I knew this, and have always done it in that right order but somehow didn't do it that way yesterday.

Doing a google search for battery disconnecting and alarm brings up other make forums (notably Vauxhall) where the advice is to disconnect the battery while the key is in the ignition and turned to position 2, or to turn key to position 2 and take out, and quickly disconnect battery in 15 seconds.
Anyone tried that with a mid 90's Mercedes ?

If you can do it THAT quick - I'd apply for a job with a F1 pit crew.!!

 

[eyelight]

If you can do it THAT quick - I'd apply for a job with a F1 pit crew.!!

Well it would only be one terminal. Could be done.
Would be best though to have the help of an assistant. My assistant today is my 11 month old daughter, and though she's a quick learner, I don't think she's up to elementary car maintainance yet.

 

[JEZ.S320L]

Well it would only be one terminal. Could be done.
Would be best though to have the help of an assistant. My assistant today is my 11 month old daughter, and though she's a quick learner, I don't think she's up to elementary car maintainance yet.

Can I video the attempt, for you? I may be able to get £250 off Harry Hill, afterwards. LOL

 

[television]

There is a very good reason why the flat battery should not be charged when joined up.

In order to start the flat battery charging the voltage sometimes would need to get to 20 volts, it is this what does the damage to the car electrics.