Subsea power sources and related systems include a housing having at least one first magnetic member, an internal member having at least one second magnetic member, and at least one elastic member positioned in the housing. Movement of the one or more second magnetic members relative to the one or more first magnetic members, which can be obtained by positioning the power source in a subsea environment such that forces therein contact and move the housing or internal member, produces an electromagnetic output for powering a subsea object. Contact between the internal member and one or more elastic members causes the one or more elastic members to impart a force to the internal member to facilitate continued movement and power generation. Power generated in this manner or through other means is usable to operate a subsea kill plant, usable to kill a well or operate a subsea blowout preventer.