I'm having issues starting it up lately.
The battery drains very quickly within a few hours when left alone. It drains often I've charged it like every other day. It did last 4 days once though. ¯\_(ツ)_/¯
It has never died completely though, the tender shows it at between 0-25%, it drops from 100 to 50% every time I try to start and it fails.
Headlights, Dash lights, instruments, media console always turn on.

I have a battery tender and if I charge it up overnight , it starts up in the morning and then dies in a few hours.
I don't think it is a fuel pump issue as I can hear the sound of the pump.
Engine cranks over fine and revs when accelerator is pushed.

Problem seems to be with the alternator, starter, spark plugs or battery (I think).. not sure how to proceed..
I don't think it's the alternator since it runs fine for any amount of time if it starts.
Any help narrowing the problem down or identifying it is appreciated. Thanks!

 

Getting the battery tested would tell you if it's the battery. I would start there personally

 

I did when I called the AAA guy the first time it happened and he said it was fine. But I'm not so sure anymore. Any way to do it at home without a load meter?

 

Not that I know of. Someone smarter than me, might know. Just take it to O'reilly's and ask them to test it for you. I'm not very knowledgeable about electronics so hopefully someone else will chime in

 

A proper battery test requires a load tester. A DMM can be used for a current draw test which would rule out excessive drain. If the problem isn't excessive drain it's very likely the battery itself.

 

I know how to use the DMM to check voltage but how do I check for drain? Try starting the car while someone else holds the DMM at the battery to check for fluctuation?

 

Nope. A current draw test will tell you how many electrical pixies are coming out of the battery when the car is sitting there with everything off. If the amount of drain is within a reasonable range and your battery is still dying then it points to a bad battery.

 

Gotcha! yup this would help a lot. Ordered a DMM I'll do this on monday.
So what kind of draw levels are standard for a miata?

 

I've never measured a miata but without something like an aftermarket alarm I'd expect under 50ma. Even with one it should be well under 100ma. To kill a fully charged battery in a day you should be at several times that.