If we use "fallen angels" to determine if angels have free will not not, I have come to the conclusion that there is not a lot of straight forward information on fallen angels in the scripture. The passages below which are used to support fallen angels are somewhat vague on the subject.
Job 2:1 - Again there was a day when the sons of God came to present themselves before the LORD, and Satan came also among them to present himself before the LORD.
John 8:44 - Ye are of [your] father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
2 Corinthians 4:4 - In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
2 Corinthians 11:14 - And no marvel; for Satan himself is transformed into an angel of light.
Ephesians 6:12 - For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high [places].
James 4:7 - Submit yourselves therefore to God. Resist the devil, and he will flee from you.
1 Peter 5:8 - Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:
2 Peter 2:4 - For if God spared not the angels that sinned, but cast [them] down to hell, and delivered [them] into chains of darkness, to be reserved unto judgment;
1 John 3:8 - He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
1 John 4:1 - Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
Jude 1:6 - And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
Jude 1:6-7 - And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
Revelation 12:7-9 - And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels . . .