I got my replacement charger after the first time check-up at the bike shop. I also believe I got one they had lying around.
@JonnyM For now just repeat the charging attempt (re-plug when you hear the charger relay switch off) until the bike charges correctly. Worked for me after ~20-30 attempts as my battery was extremely drained. Spent 30 minutes in my cozy basement compartment.
I also kept bugging Focus to issue an official statement regarding these chargers. They finally replied they could not find any general issue with this series of chargers. Must have gotten just a broken one, they said.
Unfortunate that this recurring issue will not be acknowledged and new owners will not be notified. From my perspective a recall should be issued for the 4.5A chargers.
EDIT: My apologies for the overuse of any issue-related terminology.