[-Joe]

My MGF drains it's battery such that it won't start. I have a 20W big solar panel and charge controlller fitted to my car which sort of solves/masks the problem.
I would like to find the root cause of the problem this is my thinking so far.

No bonnet light fitted.
Boot light works OK
Mirror lights off.
ECU fittted with LED on engine power circuit which shows power shuts off as it should after 8mins.
Replaced Alternator diode pack
Battery earth good.
Engine earth good.
Radio back up power disconnected- no change
Charging voltage seen on ODB2 as good.
Only things left on are petrol gauge, alarm.

I hear that the alarm system includes a Ni-Cad battery so it keeps sounding even when the main battery is disconnected. Well it makes purfect sence that this battery could be worn out and causing the discharging problem. Where do I find the thing? I wish to remove this extra battery or maybe replace it with a newer one.

 

[Chris T]

The petrol gauge takes no power, the needle will not move even if you remove the cars battery for some time.

Have you changed the battery as it is possible that the battery is internally discharging.

However I would suspect the cars main ECU isn't shutting down fully

 

[-Joe]

Have tried 2 batteries. LED on Engine ECU brown/pink wire goes off as it should after a delay, does this indicate full ECU shutdown?

 

[Chris T]

At this stage I would start using a multimeter to test the current draw of each circuit, this can be done by removing a fuse and using the multimeter set to amps, safer if you a test prob such as Gunson 77068 Automotive Fuse Adaptor Test Leads

 

[Austin2297]

If (understandably) you believe the battery is discharging when the car is locked up and not used, then this has to be checked.
Have the measured the actual electrical drain under these conditions?
If not, then you will need to do this as your first step. All things being right, then the normal drain would be expected to be no more than about 50mA once everything has ‘shut down’ - say one minute after the car has been locked.

 

[nocturneblue]

My TF drains the battery pretty fast if the door is locked i.e. alarm system is on. I leave it unlocked at the moment as it is on my drive on stands and it lasts a week, but I can see that isn't a great long term solution ;0)

 

[Austin2297]

Obviously something wrong there, which warrants measuring the amperage drain when the car is locked up. Good ball park figure when all is well would be less than, or around 50mA, measured about 1minute after the alarm has set. Of course, also worth checking the battery efficiency.

 

[nocturneblue]

Battery is pretty new, that's not the problem. I do need to check the current drain, true enough. It's just another thing to get around to! I have a current clamp so easy enough to put that around the battery lead and connect to a DVM. It's at the bottom of a list of other jobs I need to do unfortunately ;0(

 

[jonrose]

I had this on my MGTF last autumn. The battery was only a few months old and would last about a week if i didnt drive the car. It seemed to be charging properly and the current drain after turning the engine off was around 30mA when the car wasn't locked. In the end I bought a Discarnect isolator and haven't had any trouble since. Best £5 I ever spent!

 

[Austin2297]

But then you don’t have an alarm and immobiliser. We’ll forget about the minor inconvenience of having to reset the clock every time you use it.
Wondered if you bought a good quality battery.

 

[98luke]

Do you have any aftermarket items that have been fitted that would draw a small amount of current?

The reason I ask is that I have, on my own TF fitted a USB charge port in place of the cigar lighter. The cigar lighter supply is permanently live and USB charge port is always illuminated. I have also fitted a remote boot release and the concealed push button that is also connected to a permanent live and also illuminated. Both these together draw about 40mA. Not a problem for me as the car has a brand new Varta battery and also is permanently hooked up to a battery tender during winter storage.

The car is also garaged so I do not lock it and therefore there is no draw from the alarm. If the alarm is set then there is another 30-40mA drain on top of my two illuminated features.

 

[Austin2297]

Any particular reason why both these accessories are wired through permanent lives (separately fused?) rather than through the auxiliary position on the ignition?

 

[Julian Foulger]

Easy to change to 'switched' from 'permanent' if you have the cabling going to the driver's fuse box. I personally would not have the USB charge point on 'permanent' unless there is a very good reason.

 

[98luke]

The USB port was wired in place of the cigar lighter and that is permanently live. Have been meaning to move that onto a switched live at some point, but not an issue as the battery is on a battery tender.

I intentionally want the remote boot release on permanent live such that the boot can be opened without having to switch the ignition on. Handy if I ever lock the key in the boot. And yes both are separately fused.

Don’t want to highjack Joe’a post just wanted to point out that if he has some accessories that are on permanent live then these will contribute to his battery drain.

 

[-Joe]

Yes, yes, yes. What about the alarm battery thingy?

 

[Julian Foulger]

98luke.....So the boot release can be opened by anyone at any time with no key? I suggest that this is not smart.

The cigar lighter does not use charge even if not switched. But I think a not-in-use USB socket running off a perm supply does use charge via an internal switched-mode power supply.

 

[98luke]

Thanks for your comments, however, the boot release button is hidden and not on view.

Like I said yesterday, let’s try and help the OP with his problem. I do not have an issue with my battery.

 

[98luke]

Yes, yes, yes. What about the alarm battery thingy?

Joe, have you measured the current drain using a meter? You should do this with the vehicle unlocked and also locked with alarm set. Typically 50mA with alarm set. Significantly less with vehicle unlocked once the footwell lights have gone off

 

[Austin2297]

Exactly what I suggested to him 10 days ago!

 

[-Joe]

For Covid reasons I have not visited my car for 3 months. It is hibernating in somebody elses dry garage. I left it with battery unplugged. I will visit it soon as garage owners have been vacinated about 2 weeks ago. Then I will reconnect the battery through a multimeter and measure the electrical current. Thanks forum for the expect 50mA as a target of what to look for.