It is a battery fault, and I am pretty sure about it. Battery is made up by combining many small cells. Each cell has its own power and capacity. All the cells are connected in a pattern inside the battery. As an example if your laptop battery has six cells and all the cells are fully charge. When you would start using the sixth cell first drain, then after fifth and fourth. In case your third or next cells are faulty, your battery will suddenly drain to 10% or 0%. Seems like some cells of your laptop battery are dead, and it’s dropping from 60% to 7% instantly.