the check gauge light comes on while driving and the battery jumps to 19. what could the problem be?

 

A failing alternator is the primary suspect. A possibility (but less common) is a failing voltage regulator; it is located inside of the computer on a 98.

I usually verify that reading with a meter at the battery just to be sure it is real. If it is, you may want to pull the alternator and have it bench tested at a parts store. No charge for that.