Hey @robboy657 ,
The most probable cause is the battery since when the battery gets very low the phone goes into power save mode and the first things it does is turn off WiFi, Bluetooth, and GPS. If this is not the case, can you check your Power Saving settings and change them to see if that helps? To do this help into Settings> Device care> Battery> Power mode.
If you think that there is anything wrong with the phone you can run a check on it from
Samsung Members > Get Help > Go to Phone Care > Interactive Checks> Wi-Fi/Bluetooth.