Aspis is the only unit out of the Shieldbot Factory that requires energy to recharge.
Felons do not require energy directly, but as they expend their own shields to attack they can keep shooting by transferring shield power from your Aspises, which then require energy to recharge. The basic shield transfer mechanics mean Thugs cannot recharge Felons past 1200 shield strength, and a fresh Aspis charges Felons more rapidly than just Thugs would. So if you do have a shield ball with Aspises and Felons, the Felons will unavoidably spend shield charge shooting that will require energy to replace and that's generally a good thing because it means the Felons can keep up their full DPS for longer.
