By MIGUEL BUSTILLO and DAVID R. BAKER SPECIAL TO THE TIMES Michael Halsell, the Newbury Park teenager who was critically burned over 85% of his body while climbing a 175-foot electrical tower, died Monday after what doctors are calling a valiant two-week struggle to stay alive. Michael was pronounced dead at 8:55 a.m. at Sherman Oaks Hospital’s Grossman Burn Center as his parents, Hal and Bonnie, and his brothers, John and Chris, kept vigil at his bedside.