I think the Russian word "volya" can properly be translated either as "freedom" or "power." When we talk about freedom of the will, whether or not we are Russian, we are talking about both.
So far as the power to achieve our wishes is concerned, the notion of free will is very much confused by theological notions about double predetestination and/or original sin. The soul does not even have the power to choose salvation because original sin has compromised the will, absent God's grace, much less to actually perform any salvific work. Nonetheless, predestinationists hold God has predestined the elect to freely choose salvation and the damned to freely choose hell.
Non-Calvinists, thinking that a soul without the power to freely choose is not in fact free, as will implicitly means the power to choose, reject double predestination. The scriptural proofs for Calvinism depend upon an elaborate exegesis. But, since Calvinism requires tacit supplementary theological assumptions to fulfill the presumption that the Bible in fact truly has real doctrines to impart, anyone who fails to accept the tacit presumptions is unconvinced. The Bible is a collection of documents by different authors with different ideas which in the end are not fully compatible or are in fact outright contradictory. By the same token, there are necessarily proof texts for a wide range of position. So the Calvinists cannot refute the Calvinists on Scriptural grounds. However, although Calvinism has never been refuted, it is out of fashion.
Thus, most modern Christians just flatly declare that free will exists. This merely reflects the fact (invariably, in my experience) that most Christians detest actually reading the Bible, on the sensible ground it is too difficult for them to understand. Concluding that God decreed what the Christian personally believes is not sensible, but---judging from all appearances---immensely gratifying.
In an SF forum, the notion that the immutability of time refutes free will is a very common one. Apparently, the overall plot of the Dune series lies in the notion that mankind will be set free if prescience of the future is abolished. Apparently, men must be able to think they have the power to change the future if they wish. Generally, time travel plots that hinge upon the impossibility of changing time are regarded as downbeat or even tragic. Free will is held to be the power to choose, regardless.
Personally, I think free will is more like the franchise. If you choose your candidate, even though you cannot determine the outcome of the election, then you have a free franchise. If you cannot get your candidate on the ballot? Well, then, you are effectively disfranchised.
Similarly, with free will---if you can make a meaningful choice, you are exercising free will, even if you don't have the power to achieve the choice. (This has similarities to Camelopard's ideas above, by the way.) But I think putting it this way emphasized the importance of thought. It is not free will to imagine flying, and then actually flying. It is free will to think---plan, build airplanes or at least buy a ticket---then to fly. With greater knowledge comes more freedom, both in the power to achieve goals and in determining which choices are in fact meaningful.
Now, as to free will as the ability to choose unconstrained by the brain---truthfully, this seems completely mad, a totally ideological misconception of reality. It seems to be some weird acceptance of the soul as some nonmaterial, eternal entity. Instead, mind is produced by neurotransmitters and electrical activity of the brain as flame is produced by the chemical changes in combustion. The effects of drugs or damage to the brain may be to deprive me of free will.
Even more to the point, psychological studies of the timing of events and neural activity pretty reliably show that the brain makes decisions (showed for example by beginning a muscular movement as in reaching for an object) before subjects report deciding! This shows two things I think. First, that our minds are not just pure consciousness (something we knew from dreaming I should have thought.) Second, that the will, in the sense of freedom to choose, is a determinate event. (No, I can't remember the names of the experiments and experimenters. Sorry.)
People committed to the pure soul, unconsciously or not, will be distressed. But, to be determinate is one aspect of being real. Something indeterminate, like the quantum mechanics proposed for consciousness, is in a sense to be something unreal. Better to be real. In any event, there is plenty of role for free will, in the sense of the conscious, reasoned decisions that we make.