I wired up my parallel, dual 18650 external power source for my ELPH 300 and gave it a try but it has been unpredictable. My batteries are good, 3.7v protected cells, I often use them in my diving lights and they work flawless.
When I use it with the camera, connected to the dummy battery, it will always take a pic or two then more times than not, the camera will go silent. The camera appears like it's in a dead battery (lens out but no camera operation) state but pressing the play button will initiate a restart, no other buttons illicit any response. It seems to happen most often when I have the camera sound mute enabled and the backlight turned off via script. If the camera is able to go a few minutes running without this freeze up then it's clear sailing.
Last successful use was about 4 hours of yass script interval shots and the battery meter still displayed 80%.
I have another build to finish that will use a small sealed cell 12v battery through a Buck voltage regulator but it not air travel friendly.
Any ideas?