I recently purchased a used '96 Miata with 61K. Love the car. I've put about 1000 miles on it during the past few weeks and everything has been perfect, until Saturday night...
I stopped at a local tavern with a friend to get a bite to eat. A couple hours latee, we're getting ready to leave and the battery is dead. No hint in advance whatsoever. The condition was similar to what you would see if a connector on the battery had become badly corroded, but that was not the case. We push-started it and drove about 10 miles, ran great, all electrical worked fine (including all idiot lights), which would appear to rule out an alternator problem.
Got home, turned it off, not enough power to crank the starter, not even a groan. I slap the charger on it and it doesn't want to charge because the battery reads 12.75 volts. There's enough power to run the radio, but turn on anything that draws amps and it's no-go.
I put a meter between the battery positive and the battery cable and it seems to be drawing 6 milliamps cold, which I understand is within specs since I don't have an alarm system. That appears to rule out a short.
I tried to jump-start it with a '95 Accord and couldn't quite get it started, the starter would turn a bit but I think the resistance of the jumper cables was too much to get enough amps from the Accord. Running the jump car for a while did not appear to charge the Miata battery at all (no surprise there given the driving experience).
The battery appears to be a Mazda replacement acid unit (it's got vent hoses and there's a warning on the top about acid) but maybe I'm wrong about that. I haven't spoken to the previous owner. I'm left to conclude that it is a simple battery problem. Given the fact that I have to push- start it and can't turn restart it if I turn it off, I need to do something and replacing the battery is the quickest and least-expensive "fix."
Any ideas? Thanks.
dm