Some times it is the simple things. While I had the battery out to fix the issues in the battery box on my 924s I made sure to clean the posts as well as the clamps on the leads really well. It is amazing how much better the car runs. More pep. starts better idles better.
I know common cense and I should not be surprised. And I have done this before to other 9444's with similar results. It is just great when such a simple thing makes such a great improvement to a car.
And clean any ground wire that you find. Everything works better with good grounds.
And slather some grease on all the exposed metal (cables, terminals, clamps) of the cables at the battery.
baking soda is great stuff, just one of it's many great uses
I don't know how many no-crank, no-starts I fixed by cleaning the terminals. Usually didn't even require a jump, just the requisite connection haha. And yea, clean the grounds too.
I've cooled many pissed off customers (big box parts store) by going out and cleaning/tightening the battery cables when their car won't start.
Also scrub the top and down the sides a ways with some baking soda and water(then rinse heavily), the whole top of the battery builds up conductive gunk and causes a parasitic drain.