Oh ye of little faith. I'm sure Miele may well release a stronger, longer lasting battery in time. In light of cordless stick vacs running out of puff early on, the Hoover Linx/Vax Linx and current models from other brands who are using longer power run lithium batteries are much better than what went on before.
Depends on the amount of dirt you're cleaning up with, at least Miele have something here compared to other brands like Hoover or Electrolux that don't offer the option of a powerhead with its own power on board, even if you have to charge the battery when it runs out.