I am Samuel and I will help you. Did the prior owner have the same issue with battery life?
Ok it is hard to determine battery issues when the battery is not accessible. So we have to assume it is either a software glitch causing the device to run harder than it should or a hardware issue (which for a S7 edge will be costly). To repair a glitch or corrupt software you should do a factory reset. Yes, this does remove all information that you have on the device that is not saved or backed up.