The Extended Range Air Supply allows your dives to be longer before you need to return to the surface for air replacement.
Additional information
With a SportSub’s standard air supply, you can expect a maximum submerged time of 2 hours. At that point your air supply will be depleted. Because SportSubs use standard scuba tanks for their air supply, you can easily remove the empty tanks and replace them with full ones. Your batteries have considerable capacity so you can repeat this procedure many times each day. The 3 person Subs gain 200 ft3 of additional air supply while the SportSub II gains an additional 160 ft3.