Constant flat battery

  1. My model of MX-5 is: NC1
  2. I’m based near: __
  3. I’m looking for technical help or recommendations on: Flat Battery

I have a fairly new (to me) NC1.
The previous owner had the battery changed recently.

My car cannot go more than 4 days without discharging the battery. It’s a weekend car so not used day to day.

Key points -

I have witnessed the car alarm triggering by flashing it’s lights (no alarm sound) on several occasions. I can only presume this is happening when I’m not there to witness and it persists until the battery is flat.

I have read historic accounts of this type of behaviour but couldn’t see a reliable fix apart from the following that I have tried

  • lock car with key not fob
    -turn off internal detection with button on fob when locking with fob.

There’s also talk of faulty bonnet or door sensor?

I’m at a loss. I’m hoping it could be a simple case of wrong battery fitted?? But I think I’m hoping for an unlikely outcome there. It’s probably a red herring and the battery was replaced due to this fault by the previous owner.

Any experience or suggestions?

Typical triggering of the alarm can be if you left a device in the car which is connected to a data network. Others and myself have done this, within around 5 mins off goes the alarm. Not sure about just your lights flashing, no alarm situation?
Could there be a device somewhere in the car, or one of these Chinese head units that auto detects a signal.
I know if I move my car out of the garage (next to the house) it sometimes triggers Spotify or Amazon music to play on the android phone in the house if I leave Bluetooth on.:grin:

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I read about devices triggering the alarm.

No devices. Head unit and alarm are standard equipment.

No sound just repeater/ hazard lights flashing

Simple thing is to check the earth clamp on the battery, check its tight. Loose clamp can cause discharge quickly.

Also check condition of alternator; with a diode blown, the alternator can suck juice from the battery.

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I will definitely look into that.

Would a lose earth wire cause the lights to flash? As I’m 99% sure it’s that causing the battery drain so need to fix that fault.

Have you heard the alarm - does it work? Could it be the battery gets to such a low state of charge it starts the lights flashing? You may have a parasitic battery drain problem. I would make sure the battery is correct for the car and then get it load tested to make sure it’s not faulty.

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