[BUG?] Taking picture with flash in low charge state causes shutdown

I totally agree, it'a a matter of battery not phone. Iper professional reflex are declared to works from 0° to +40° or 45° or some, because of battery. Sure yo can use one of it also at -30° but the battery discharge very very fast. The requested current taking a pic with flash probably pushed the phone to shut down especially because battery level was quite low at that moment.

I am suspecting this myself and thus wrote the report with 'hardware' tag. Here I consider battery as part of the phone. Not sure if "bug" is the right term for this as this might not fix? We propably need more people to confirm this and an answer from Jolla support to conclude as noted by rsainio.

Not being Jolla tech support, but having worked with batteries in outdoor applications, maybe I can shed some light on the battery side of things. The battery is indeed a component of the device, but subject to its chemistry, which you really can't do much about. Cold affects li-ion batteries by increasing internal resistance. In simple terms: the more power you draw, the more the voltage drops. The camera app causes power draw, so does focusing in poor light (lots of CPU use + the focusing system, which may be a bit stiff) and the flash puts an additional load on the battery. Decreased voltage makes the phone draw even more current, which drops the voltage even further. This ends either in an equilibrium, which drains the battery rather quickly, or the voltage dropping below the cutoff point - i.e. the phone thinks the battery is dead. This happens more rapidly than a normal discharge, so you don't see any low battery warnings.

I had this case today with my Jolla, but indoors with battery discharged down to less than 10%

I would suspect that also in this case the current peak of the flash is so high that it makes the system voltage to drop under the critical limit and causes the shutdown.

It could also just poor HW design of the flash circuit i.e. with led flash there probably is no need for extra capacitor to provide the energy for the flash, which could be slowly charged up to provide the flash capability and thus avoid the voltage drop on system/batter voltage.

Perhaps it would worth while to check and monitor at which charge state the Jolla will shutdown when taking the picture with forced flash in use - what do you think?

Perhaps the headline of the question could be also updated as the issue is clearly not related to cold temp, but the charge state of the battery which can be poor in cold weather, but also truly discharged like in my case.

It may be better to restrict the usage of flash completely after the certain level of Depth of Charge has been reached and indicate that to the user somehow.