Right now, multimeter across the terminals.
Even dead batteries will have some trace voltage or amperage.
I could "back yard it" by drawing some out of each cell and squirting on the grass somewhere here at work and see what the after affect is after a few days.
I could get litmus paper, but that'll just tell me if its acid or base.
My mixing ratio is loosely based off a demolitions class I took many many moons ago, where A X B + P = amount, or Acid volume X Baking soda volume + Plenty extra. I'm going the overkill route with neutralizer.
At some point it will be waaaaaaaaaaaay less caustic and corrosive than what the state puts down on the roads after a snowstorm.
If it was a maint-free car battery or lawnmower battery I wouldn't even bother. Those really aren't worth the effort, and for those trying to justify cost, it would pay out more to run it to the scrapyard or as a core.
So far its cost me $6 for an unknown amount of lead yield. I can say that the empty one (or was empty before the baking soda mix) had some heft to it. Definitely was a two hand lift, and I don't exactly have noodle arms.