Even after a day of bluetooth-tethering with a few hundred MiB transfered the battery was only half empty. N9 and N95 before never managed that

However, it seems that after disabling the tethering, wifi has issues reconnecting. Wifi is quite buggy anyway in the current Sailfish release, so I guess it's not even therering-gui's fault. A reboot fixes it, but perhaps less drastic measures are enough. On the N9, restarting the ICD2 service often helped. Is there something alike on Jolla?