Dead Battery Pack........How to tell?

Have two old Makita cordless drills, a #6012HD & #6095D.   Both use a Makita #9033 Ni-MH battery pack.  I finding that the packs won't take and hold a charge anymore. 

FIRST:  How do you tell that a battery pack is finished?  Or have I answered my own question?

SECOND:  Would you buy NEW battery packs for these drills or go ahead and replace the drills completely?

THIRD:  If you were going to buy a NEW cordless drill, what brand would you lean towards?  I like contractor grade tools.  Want something that will last.

Yes, you've answered your own question.  When the batteries won't take a charge or hold a charge, they're used up.

Checking Amazon.com I note that replacement batteries start around $25.00, so that's not a huge price.  If the tools have been running OK, I'd continue to use them.  Those Makitas are older, but if they serve your needs, and still work, I'd chose to continue using them, rather than buy new.