My 2014 Roomster has had a problem for a long time, if I don't use it every day the battery goes flat, before you ask, yes the alternator is charging OK, the battery is only 2 years old and does hold a charge off the car, I have 2 batteries, one full charged on standby, today I tried a bit of investigating, getting the meter out I find that there is a 1/2 Amp drain on the battery all the time, can't find anything that is causing it, the only thing that is on all the time is the alarm, if I remove Fuse number 20 (which is for the alarm) will that prove me right or wrong, or is there another way of switching the alarm off, any ideas?

I once had a car that did this and the boot light was staying on, I had to drop the seats to find out. 

How did you connect up the meter for checking for a drain, and how long did you leave it connected while checking the current drain current value?

I connected a meter between the negative conection on the battery and earth, it showed a steady 1/2 amp drain all the time, this has been going on for a while, if I don't use the car every day the battery loses charge significantly, I bought a new battery which was the same, so I went back to the garage they checked it and said it's fine it must be your alternator, it isn't, the alternator shows 14/15v when the engine's running. when you connect the battery earth connection up, you get quite a spark, which I don't think you should. I've tried all the boot light and glove box lights they are not staying on, any ideas?

 

I forgot to say I'm resorting to a solar charger on the dasboard, which seems to just manage to keep the battery charged up enough .(when I remember to plug it in)

You have not answered how long you take the current measurement for, "all the time" is not helpfull for the reason the question was asked.

 

These cars always create a big spark when the battery is first connected, that is normal, when you take the current measurement you must have all the doors and bonnet closed or the latches closed onto a screwdriver or similar to fool the car that everything is locked, the current should drop after 20 minutes, people say 3 hours, its been written so many times that it has been believed but its actually 10 minutes, 20 maximum.

 

A diode could have failed in the alternator rectifier which would give a current draw like the one you are seeing whilst still charging at 14.4v, you should try disconnecting the alternator & see if the discharge stops, do the same with the alarm, the internal back up batteries fail & leak acid onto the PCB and can drain current.

 

What radio does the vehicle have? Is it an aftermarket one & was it fitted recently? They can cause battery drain problems via the Canbus Gateway.

 

Has any other work been done recently on the car, any electrical parts replaced?

Is there anything not working properly, from rear wiper to a lock that doesn’t seem to work.  

 

 Roomsters seem to have very poor wiring loom (cables break where they flex in the rubber bellows at the door and tailgate hinges) and this can cause shorts and battery drain. We had to have our tailgate wiring loom replaced as rear wiper was coming on randomly and boot lock stopped working.  Exactly the same, had to use battery charger every few days until we got it fixed.

 

That thought had occurred to me also, not sure about the Roomster but on other models the drivers door window motor and the rear wiper motor are both canbus nodes, it could be if the can gateway does not get a sign off handshake signal from one of them that it does not shut down, thats exactly what happens with the aftermarket radios.

 

I'm probably way out on my speculation of why a fractured door bellows cable causes havoc but its well known that they do so definitely something to check.

On 23/02/2022 at 20:17, Locomotive said:

My 2014 Roomster has had a problem for a long time, if I don't use it every day the battery goes flat, before you ask, yes the alternator is charging OK, the battery is only 2 years old and does hold a charge off the car, I have 2 batteries, one full charged on standby, today I tried a bit of investigating, getting the meter out I find that there is a 1/2 Amp drain on the battery all the time, can't find anything that is causing it, the only thing that is on all the time is the alarm, if I remove Fuse number 20 (which is for the alarm) will that prove me right or wrong, or is there another way of switching the alarm off, any ideas?

Remove fuse 20 and put your current meter in series with the contacts where it plugs in, see if there's half an Amp going through it. 

You could measure mV across its ends with it still in position if it's the fuse type that has exposed metal pads on the top surface, see here: https://www.briskoda.net/forums/topic/377587-technical-bulletin-about-parasitic-current-draw-measurement/

 

 

Measure all the other fuses if that one doesn't register any mV. I've personally found in a few cars I've looked at that 30 minutes is a good time to leave things to shut down, and that having doors open and car not locked doesn't matter. May well vary with model.

Thanks for the replies to this topic, they've given me plenty to think about, in answer to some queries, the radio is original, nothing electrical has been added, everything is working as it should, except for the current drain, I'll try leaving the meter connected for an hour to see if it drops,