'Tanks are refillable energy containment systems which allow users to hold additional stores of energy for emergency situations.

Sub-tanks are a fairly common form of energy tank that hunters depend on. The sub-tank is linked to the user's body and when activated sends a flood of energy into the user's body to restore their microfusion core's shielding to full strength as well as boost the reploid's own natural repair systems. (Some models of sub-tanks also have built in nanobots to help facilitate the healing. These sub-tanks are also extremely effective on humans too, allowing the hunter to heal most wounds a person could sustain in only a matter of minutes.) Because of how useful these tanks are, most hunters armors have slots for up to 4 sub-tanks.

4 is an optimal number, allowing for a lot of healing while not causing a shortage of sub-tanks for other hunters. Though in shortages, some hunters volunteer their sub-tanks to others to help keep them safer. X and Zero are both known to do this.

Weapon tanks (W-Tanks) are refillable tanks that link into the user's onboard weapon module system. The weapon modules gathered from defeated mavericks have only a finite amount of energy before they are exhausted. The W-tank completely recharges all the weapons energy to maximum. Though in doing so it uses all the energy it has stored and cannot be replenished easily.

These tanks aren't standard issue for most hunters, they have to be specially ordered. And the hunter's armor (unless it was designed for W-tanks) usually has to be modified to allow the integration.

Subtanks and W-tanks are powerful tools in the games, allowing for more health. Though in the roleplay they are often viewed as “get out of jail free” cards that allow users to take powerful hits but not be completely killed for it. Because of this, sub-tanks are generally not handed out 4 all at one shot. They usually are dispersed throughout the game leading up to 4 at the very end.

Also of importance is that while on mission in the RPs, sub-tanks cannot be refilled… Except by one player sacrificing their energy to give to another.