Anyone experienced this? f15 50i

[50i]

Stopped for gas then when i came back into the truck to start the vehicle. Power went out, start button is not responding. Had to call for a jump. It started but a few miles the truck shuts down again had to wait for another jump was barely able to reach home. Isnt it suppose to keep running even if the batteries have no power as long as the engine is on? TIA

[Danyal.N55]

When I got my 2016 X5 xDrive35i I parked it outside my garage and turned it off, and I came out 45 minutes later and noticed the Headlights were on and the key wasn’t responding and doors weren’t opening or anything. So I left and came out 15 minutes later and it fixed itself somehow.. My assumption is get a new battery as when you turn off the car the car goes into accessory mode then hitting it again with ghe foot off the brake shuts the car off fully.

[50i]

Car was completely off while i was filling it with gas. I replaced my main battery waiting for the aux battery to arrive. Whats confusing was why the engine died when it was already running after it was jumped. Checked voltage after replacing batt and is at 14.2.v which indicated charging.