mobile

Ok so i noticed a week ago that when i record a videi more then 2 minutes long, my phone freezes, and i have to remove and insert the battery to start it up again... then after i turn it on it has 10-15% battery life, and sometimes even less... (the phone freezes no matter hiw much battery i have, today i tried it again at 76%, and after the freeze it dropped ti 14%. Also another problem i noticed is that sometimes when i have low or medium battery life my phone starts to flicker and its really weird, and i noticed my battery is draining faster then usual... my phone is 2 years old now, does anyone know how to fix it ? Would a new battery fix everything ?