The battery draining shouldn’t affect the downloaded content.
The only thing possible I can think of is if you are downloading to an sd card. On some devices, it can take a bit of time after booting up before the card is ready. If the device is like this and you check Downloads during this time, the app would not see the content so it might think it is empty, although it should say something like “storage not found” in an error box at the top of the page.
Force stopping the app and restarting after the card is ready would fix this.
