system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Why was the Death Star II bigger? Was it supposed to be more powerful? Is one shotting any planet not powerful enough?
gpt
It was partially about a more versatile design, but having a bigger death star did solve some practical issues, too. The first one had a single reactor who powered everything else in addition to the superlaser. The Second Death Star had three reactors, one purely for powering the Superlaser.

This meant that while the First Death Star required 24 hours to recharge after cracking a planet, the Second one can destroy several planets a day! Now that's efficiency!  
On a more serious note, the Second Death Star had much more precise targeting systems to let it target more mobile targets than a planet, like capital ships.  The dedicated reactor meant it could fire less-powerful blasts at capital ships with mere minutes between the shots.