DeWalt Tools, Replacement Battery question?

I have a DeWalt drill the wife bought me probably 15 years ago, it came with 2 batteries and it is still going strong.
It seems like a battery will last for 6 months or more, and I use the drill almost everyday.

I also have alot of M-18 tools, the factory batteries seem to need charged after a hard days use.
But the tools probably have more draw, weed-eater, skill-saw, saw-zl, hand grinder, impact gun.

Battery powered tools are handy, just grab and go.