Bem, de acordo com a entrada de Wookiepedia na Estrela da Morte :
The Death Star's superlaser derived power directly from the hypermatter reactor. Its faceted amplification crystal combined the destructive power of eight separate tributary beams into one single blast with the intensity of a stellar core. After firing a blast, though, the Imperial engineers had to recharge the reactor, which took at least 24 standard hours. Though the energy output of this blast could be scaled to fire at smaller targets such as capital ships, as was the case during the Rebel assault on the second Death Star, the two major instances in which the superlaser was fired were at full power at planetary bodies.
(ênfase adicionada)
Agora, não vejo exatamente a fonte da informação, mas a maioria das coisas no Wookiepedia deriva da informação bastante extensa nas publicações do Star Wars Extended Universe, que incluem especificações técnicas e assim por diante.
Eu acho que a maior parte veio do romance do mesmo nome .