Depending on your city there might be electronic stores or stores selling travel necessities which offer external universal smartphone battery chargers.
For the Fairphone 3/3+ battery the charging contacts have to be thin enough to be able to reach the battery contacts, this is not a given with all universal chargers.
If such a charger can be bought directly in your city, then this would be a fast way for the user to charge the battery, and for a device with a removable battery an external charger is good to have around anyway (as can be learned from this case).
Here’s a topic with some mentions … External universal chargers for Fairphone batteries