Has anyone had any luck with third-party batteries? Which model batteries have you tried? Does Sailfish OS, as distributed on other phones, need any changes to optimally run third-party batteries?
Jolla Customer Care has asked me to share that I've used a battery originally designed for ZTE devices (replacement part no. LI3719T42P3h644161) to boot an unresponsive Jolla handset. The battery was 3.7V, 1850mAh and roughly 64mm by 42mm by 6mm with the correct pins and safety catches to fit into the battery slot. I successfully ran a few apps without issues, but haven't been able to perform further tests.
I haven't checked if Sailfish OS does anything special with regards to battery monitoring, charging and safety. I don't know if it expects to query a controller on the battery's PCB, or has been hard-coded to standard operating conditions (temperature, peak voltage etc.) for the 22B50 from NLT Electronics.