Starting Problems

Despite what you've said, I'd suspect battery still. Can you test the voltage of it? Does your charger indicate battery health at all?

I've had a new battery in my T-Bird (commander) every 18 months or so since new, despite being kept on an optimate.

 

I find that it's not using it that kills the battery most.

Also, check when you're attempting to start it (and it's clicking), do the lights on the gauges fades? If so, it's almost certainly the battery.

If everything stays nice and bright, the starter motor just doesn't turn over ... then yes, it's quite possibly not the battery.

 

It has pretty much all been said. A smart charger will pay for itself by making your batteries last well over twice as long and putting that tedious ‘click, nothing’ firmly to bed. Try starting a car with such a tiddly battery with minimal reserves of power.

 

You have maybe never noticed but pressing the starter disengages the headlight as it engages the starter motor. If you leave the ignition on the headlight will dull quick enough.