Voldemort was in the center of the battle, and he was striking and smiting all within reach. Harry could not get a clear shot, but fought his way nearer, still invisible, and the Great Hall became more and more crowded as everyone who could walk forced their way inside.
Harry saw Yaxley slammed to the floor by George and Lee Jordan, saw Dolohov fall with a scream at Flitwick's hands, saw Walden Macnair thrown across the room by Hagrid, hit the stone wall opposite, and slide unconscious to the ground. He saw Ron and Neville bringing down Fenrir Greyback. Aberforth Stunning Rookwood, Arthur and Percy flooring Thicknesse, and Lucius and Narcissa Malfoy running through the crowd, not even attempting to fight, screaming for their son.
Voldemort was now dueling McGonagall, Slughorn, Kingsley all at once, and there was a cold hatred in his face as they wove and ducked around him, unable to finish him - Bellatrix was still fighting too, fifty yards away from Voldemort, and like her master she dueled three at once: Hermione, Ginny and Luna, all battling their hardest, but Bellatrix was equal to them, and Harry's attention was diverted as a Killing Curse shot so close to Ginny that she missed death by an inch -
He changed course, running at Bellatrix rather than Voldemort, but before he had gone a few steps he was knocked sideways.
"NOT MY DAUGHTER, YOU BITCH!"
Mrs. Weasley threw off her cloak as she ran, freeing her arms, Bellatrix spun on the spot, roaring with laughter at the sight of the new challenger.
"OUT OF MY WAY!" shouted Mrs. Weasley to the three girls, and with a simple swipe of her wand she began to duel. Harry watched with terror and elation as Molly Weasley's wand slashed and twisted, and Bellatrix Lestrange's smile faltered and became a snarl. Jets of light flew from both wands, the floor around the witches' feet became hot and cracked; both woman were fighting to kill.
"No!" Mrs. Weasley cried as a few students ran forward, trying to come to her aid. "Get back! Get back! She is mine!"
Hundreds of people now lined the walls, watching the two fights, Voldemort and his three opponents, Bellatrix and Molly, and Harry stood, invisible, torn between both, wanting to attack and yet to protect, unable to be sure that he would not hit the innocent.
Harry Potter and the Deathly Hallows (The Flaw in the Plan)
What makes me wonder (and worry), is that Molly Weasley joined the second to last fight, and only then did she remove her cloak. She was in the midst of a battle, right in the center, very near to both Voldemort and Bellatrix, and she still had her cloak on. Why? Wouldn't the cloak slow her movements? She could have been healing people but the fact that she could have hit by a stray killing curse because she couldn't dive or that she could have hit by a stray Bombarda or Reducto because she couldn't bring her wand up to cast a Protego still worries me. And even then, no Death Eater would ignore the chance to kill someone just because he/she was healing people.
Was this an oversight on J.K. Rowling's part? If not, why did Molly still have her cloak on throughout a vast majority of the battle?