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Over the past few days my NA8 has been difficult to start after its been left for more than 8 hours or so without being dríven.

The car turns over very very slowly when I try to start it, once it fires up it'll run fine (but the battery is now so flat I can't get it to start anymore after being left for around 12 hours). After I had come home from uni I turned the car off and attempted to start it immediately after, the motor turned over at a much more healthy pace and fired up straight away.

Is this just an old battery that needs replacing or could it be a problem with the grounding or something else? I have no problem springing for a new battery I just don't want to replace it and then find out it wasn't the problem.

Cheers

Sounds like a battery to me. Any idea how old it is?

No Idea how old it is, I've had the car for a few months now. I'll go about replacing the battery and see what happens.

eunos wrote: I'll go about replacing the battery and see what happens.

I suggest, if you haven't already, that you do a search in the forum for a recommended battery. As you know the battery sits in the boot and therefore needs to be vented. This achieved via two hoses that attach to the battery and then to vents in the floor of the boot. There are not many batteries that allow for venting in this way. While the factory battery is expensive at $200+ I have had one last for over 13 Years, which is more than double the life you would expect from a normal battery. There are other options that you should find in a search.

J

Before you spend any money on it, check that the contacts are nice and clean, and that the earth strap from the negative terminal of the battery is making good contact with an unpainted part of the steel body.

If you don't have one, borrow a battery charger and give that a go too.
If your MX-5 is only dríven sporadically, then having a flat battery is to be expected, so putting it on a trickle charger when you're not using it would be a good idea.