I’ve left them in the charge case for a week and as far as I can tell, they were fully charged and the charger still had a couple more charges remaining.
Small lithium batteries don’t tolerate long term storage at full charge. I have a large number of lithium polymer batteries including over 30 from 70 to 200 mAh capacity and numerous larger ones. Their longevity is extended by leaving them partly discharged when not in use.
I would hope and expect that Bragi limits the maximum and minimum voltages of the Dash batteries to mitigate damage caused by leaving the units in the charger for extended periods or by permitting excessive low voltages should you fail to put them in storage mode in a discharged charger.
My Drone batteries have internal circuitry that automatically trickle discharges the battery to about 60% charge if I don’t use them within two days of fully charging them, but those are likely charged closer to their absolute maximum. Still, the 60% storage capacity is useful for extending the life of these sealed units.