Fusion cores - general advices
Fusion cores can be found in various locations across the whole Commonwealth. Most frequently you can find these items in generators located usually in basements of larger buildings. They can be also found in Power Armors left in various parts of the wasteland. Don't forget that the more to the south you will go, the more dangers you will find on your way.
It is worth remembering that core fusions can be bought from almost every weapon merchant.
Nuclear Physicist perk impacts the effectiveness of core fusions - on rank. 3 it doubles the amount of time during which the core is working.
Repair bobblehead can additionally increase the time during which core fusion will work by 10%.