As the title says is their any tell tell signs that the battery is on its last legs or the alternator has packed in?



A bit of back story will help...

So about 3 months ago I'm leaving my SO's house and the MX5 is flat. Stereo, lights and alarm all work but it just didn't have the juice to crank it and it seemed odd as the car was driven to her home the day before (some 30 miles) and we had only just come back from shopping. I just put it down to maybe leaving something on. We just jump started it and its been fine till about a week ago. The car had been sitting on the drive for 4 days while I waited for parts to repair a water leak. I just put this down to the car sitting while the alarm slowly drained the battery. The only thing that seemed odd was that it only took an hour to charge from totally empty to half full that seems really quick to me compared to other car battery's I've had to charge. Then today it drove fine to and from work but on the way home I had to turn it off and hop out to quickly to move another car then when I went to restart my car nothing, lights and stereo worked but just could not turn over.

I'm tempted to say its the battery due to how its gotten worse over time, if it had been the alt it would be a case of it never starting on its own after that first event.

I cant splash out on a replacement battery till next payday so I'm going to trickle charge it till then however if someone can chime in and tell me I'm spending money in the right area that would be great.