Os naipes do filme são alimentados por bateria. Rita sabia que Cage ia morrer, então ele não precisaria disso. Então ela só tomou para si (no caso de ficar sem energia).
Editar:
Não é uma fonte oficial, mas consegui encontrar este artigo no TechCrunch.
Battery life was also a critical concern. Liman suggested that in the movie, world battery technology has taken a major step forward to enable these battle suits to operate without being plugged in, but “as futuristic as “Edge of Tomorrow” is, it’s not unintentional that Emily Blunt steals Tom Cruise’s battery the first time they meet on the battlefield; we’re always going to be looking at our battery meter and wishing we had more juice.