Air-independent fuel cell and battery powered submarines are not at all a replacement for nuclear submarines, nor even really competing with them. No matter how good the tech becomes, diesel-electric subs running fuel cell AIPs will always have shorter range, less submerged time, and lower speeds than nuclear-powered submarines. Each time they surface, even to periscope level, the chances of detection go up massively.
That's why diesel-electric submarines are best suited for coastal defence, especially of small countries, whereas larger countries with huge areas of territory to protect benefit from having nuclear submarines.
Whether it's the right decision for Australia to get these subs under AUKUS is a fair debate, but it's not at all accurate to claim that they're using 'old' technology that is being superseded by AIP.
That's why diesel-electric submarines are best suited for coastal defence, especially of small countries, whereas larger countries with huge areas of territory to protect benefit from having nuclear submarines.
Whether it's the right decision for Australia to get these subs under AUKUS is a fair debate, but it's not at all accurate to claim that they're using 'old' technology that is being superseded by AIP.