Warning... Rookie Lavalier questions...

Is it better to get a lav that requires phantom or is self-powered? (is self-power always batteries)?

I can purchase a used AT831R from ebay for $50... that's requires phantom. How do I power it? (I assume I need a box with XLRs that goes into the XL1 but I read about the ma100 all over that doesn't have phantom power?)

... or am I better off getting a new AT831R and use the non-phantom XLR-XL1 option.

And above all that, how does an AT831 B/R compare to the Shure WL185? (I am choosing uni-directional as I'll typically be shooting one person, inside, in a small room.... interviewing lawyers or other folks for website videos.)

Thanks so much.