97 Jetta GL - Battery can't keep a charge?

I've had my battery, alternator, and starters checked, all report as working and in good condition. I've checked, and re-checked all wires and fuses, nothing is wrong in that department either. I recently took the battery out to do some basic engine compartment cleaning. Engine has 90k miles on it, and I never had any problems till I removed the battery. Now when I attempt to start the car, at times it will either:

a] not work at all - and have 0% power/amp/NOTHING.
b] the alarm will just constantly go off [having to reset it by disconnecting the battery cables themselves.]

This is a 5-Speed, 4cyl GL. I've replaced the spark plugs and wires, bled the brakes, replaced the rotors and pads, and have done about everything I can think of - EXCEPT taking it to the local VW dealerships (which are a waste of time and money - learned that with my old 95' VW Jetta GL). I've also had the battery & alternators re-checked (just to make sure it wasn't a bunch of idiot teens working @ AutoZone) - and surprisingly neither are bad and report 'as new'.

Any idea's on a solution to my problems?

replace the altanator cable from Alt. to battery.
there is a updated cable also make sure you engine harness plug is tight and has no pushed pins.

thanks for your reply! i was wandering if i can just purchase one @ perhaps autozone or advance auto? or do I need to narrow it down and find one @ a local junk yard?

thanks again!

ps - is it just called a "alternator wire" or is there a more-specific name to it?