connect to the S50, go into the config section of your S50, Advanced Features, turn on Save each frame in enhancing.
Then if the low power scenario occurs again, recharge, connect to Seestar, select Deep Sky Stack, select the images from the folder generated by your observation, and restack. There is a tutorial available on how to use Deep Sky Stack.
The saving of each frame will consume disk space on the S50 but you can delete the folder if you wish.