Battery health testing.

Aloha, I am a heavy equipment mechanic. I work with all sizes of batteries, from 6V deep cycle, typical 12V automotive, and very large amperage (usually connected in series to make 24V).
I know there are a few ways to determine the health of a battery, but I would like some input on load testers, for I would like to purchase one, and only one, if can.
I am finding different amperages available, 100amp, 130amp, and even 500amp (carbon pile). I am not sure what is best for my application.
Any info or recommendations would be appreciated.
Mahalo.