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MG MGF Technical - Battery Life

I have searched the archives and found numerous links on this area, but nothing that answers my query. My problem is as follows:

My car is a 1996 VVC, which I have owned for five years. The battery on the car will last charged about TEN days when not used.

I replaced the battery just over eighteen months ago and thought this would improve things, but it hasnt.

More recently the time has reduced to SEVEN days and this weekend, I left it on Friday night and by Sunday afternoon it was flat!!

The engine clicked when the key was turned, but wouldnt fire. I then put the battery on charge, it was showing flat and hey presto, after two hours it fired up no problem!!

My guess (not being technically minded!) is a problem with the alternator.

Could anyone confirm this and how I could test it. A cost for replacement would be helpful as well.

Of course, if I am totally barking up the wrong tree, I would welcome any other advice ref. possible causes of this prblem.

Thanks to all in advance.

Andy Beard

When you checked already all iterieur lights....

I'd suggest measuring the behavior of the brown-blue cable at the magnetic valve of the purge valve assy. (cylindric plastic can at the rear wall of the engine room).

Should close down after at last about half an hour when you stopped the engine.

If it doesn't then you found the discharge subject. New ECU required then (IMO).


Dieter K.


Many thanks.....After a trip to the MGF Centre, the problem just seemed a faulty battery (only two years old and still under warranty!!)

I hope that this solves the problem, only time will tell.

What a great place and team the MGF Centre really is. Definately recommended.


Andy Beard

Well, I too have a 1997 VVC and I am suffering a mysterious battery drain. I was browsing the BBS looking for any clues.

Batttery replaced a month ago with a nice new 50Ah Varta as I thought the previous one was the problem. Twice since then I have come to the car after being left 24 hours and battery was fully discharged.

First time on testing I thought I found a 1 amp drain through the interior light/radio/clock circuit when all was turned off. Removing this fuse shows it also enables the deadlocking system. However, when I asked the garage to check the problem had gone away.

Now, after the second failure, I have had an ammeter between the battery supply for three days turning off/on/off but cannot find a repeat.

Because linking an ammeter is a nuisance I am clipping on a voltmeter each evening and looking for a 0.2v drop indicative of a resonable drain.

The fault must be intermittant and I would like to know more of Dieter's Purge Valve and what else can remain switched on when parked.

Norman Lorton

I have just searched the archive, best phrase is "flat battery", and reason that the likely intermittent culprit is the relay unit located under the MEMS allowing one or more relays to stick on.
Norman Lorton

I've had the MEMS relay intermittently stick on causing the battery to drain. I removed the MEMS relay unit and opened it and cleaned and adjusted the relay contacts. I couldn't see any problem with the relay itself and by the time I had opened the unit the contacts were no longer stuck. It didn't stick after that for about two years. It happened again a few months ago so I fitted an LED to the relay connection so I could see at a glance if it was stuck on. As I had done the Window Delay mod it was easy to do as the wiring was already run through to the front of the car.

I found no real evidence to prove that the relay had stuck. It could just as easily have been a glitch in the MEMS itself causing the relay to remain powered on.

Another problem I had with a flat battery was caused by a broken main alternator connection. The thick cable had broken off at the alternator and was making an intermittent connection. So it charged only occasionally. Eventually the car wouldn't start and I found the bad connection. It could have been nasty because the cable is connected directly to the battery and if it had shorted to the chassis it could have caused a fire.

Bruce Caldwell

This thread was discussed between 06/04/2003 and 12/04/2003

MG MGF Technical index

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