[Borek]

What are some impurities in battery MnO2? Any heavy metals or things I should be warned about?

I have already answered this, although without quoting so it was probably not clear. MnO₂ in battery must be soaked with strong electrolyte to pesent as small resistance to current as possible. Depending on battery type this may be NaOH as jdurg wrote (in alkalic batteries) or some chloride solution in "standard" batteries (although I am not sure about details).

Note that not all types of batteries contain MnO₂.

[woelen]

As you may have concluded, MnO2 from batteries is not a very good source. It is impure, not all batteries contain this. It really is a hell of a mess to take it out (I once did this, it is TERRIBLE).

If you can find some at a ceramics and pottery shop, pick up that stuff. That is MUCH better and of quite good purity. They also carry MnCO3, which is even better. The MnCO3 usually contains a little Mn(III) and Mn(IV) species also, but with a few drops of H2O2 in acidic solution, you get easily rid of that.

[science2000]

It seems the best way to get manganese without making a special order is buying "Clear Water" from Walmart or where ever, this stuff is used to clear organic material from fish tanks. It's a very dilute solution of potassium permanganate, like under 1%. But it's very pure. but still, for $2.50, a bottle is kinda expensive. Anyone know of a better version of this that's more concentrated?

[metalriffzz]

Pond supply usually sells big canisters of KMnO4, and its used in water softeners, so if you live in the country or know of a specialty hardware shop you should be able to get loads of the stuff.