To make sure your power armor is always ready to go, you will need to have a few extra fusion cores in stock. Coming across them is not difficult but if you happen to be in this few places, here is where you can get yourself some extra fusion cores.
In the beginning, of the game after you have completed the third quest, you will be able to get the keys to Kellogg House from Nick Valentine. At the house, crouch down at the desk and you will see a red button. There is where you will be able to find yourself four fusion cores.
The fusion cores can also be picked up at the Castle but you will need to eliminate the aquatic opponents first. If you are at Ford Hagen, you will also be able to get yourself a few fusion cores at the western edge of the commonwealth at the generator room. There are also found at the Weston Water Treatment plant.
