Version: (make sure you are on the latest version before reporting):

• Minecraft: 1.15.2
• Forge: 1.15.2-31.1.44
• Powah: Powah-1.15.2-1.1.12

Issue description:

The Energy Cell (Hardened) recipe required 4 of the previous tier Energy Cells, although all the other Energy Cell recipes only require 2 of the previous tier.

I suggest you change the recipe to this, in order to make the recipes consistent:

I will add it next release, Thanks!!