Mazda MX5 Mk2 1999 - Draining Battery - Kildrummy

Our MX5 fails to start after a couple of days if it hasn't been driven. It appears as if something is draining the battery. We did have a faulty radio that would sometimes not switch off and I disconnected the radio hoping this was the problem but the problem still exists. I have tried 2 different batteries but still had the same problem. I have checked the power coming into the battery when the engine is running and I get over 14 volts.

Does anybody know how I could check the system to see if some thing is draining the battery or any other suggestions would be very welcome.


Mazda MX5 Mk2 1999 - Draining Battery - zener
I would suggest disconnecting the battery negative terminal and then connecting an ammeter in series between the negative lead and the negative battery post. The ammeter should initially be set on a 5 amp range.
Do not turn the ignition on. With all electrical equipment off, ammeter should be reading less than 1 amp. If so, move ammeter to a lower range (I.e 100ma). The expected parasitic current draw should be about 25-30 ma. If found to be greater than 100ma then battery will drain within a few days. With ammeter reading parasitic current draw, start to remove vehicle fused one by one, noting any change in current draw. If ammeter suddenly drops to around 25ma, you have found the circuit giving you the problem.
Likely culprits are alarm systems, cd changers, boot lights etc. Good luck.
Mazda MX5 Mk2 1999 - Draining Battery - Kildrummy

Thank you for your reply. I will try this out tomorrow morning and let you know the results.

Thanks again.

Mazda MX5 Mk2 1999 - Draining Battery - zener
Typo "fused" should read "fuses"
Mazda MX5 Mk2 1999 - Draining Battery - Kildrummy

should I have the battery charged up (currently flat) before doing this test or does it make a difference?


Mazda MX5 Mk2 1999 - Draining Battery - zener
If the battery is flat, it will need to be charged before you can obtain any meaningful readings from the ammeter. It may be quicker to charge the battery whilst it is disconnected from the vehicle.
Mazda MX5 Mk2 1999 - Draining Battery - bathtub tom

IIRC the number plate lights come on to illuminate the boot when the lid is open and the battery's in the boot. Don't be misled.


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