Hi, I'm not exactly sure what the issue is, but I can confirm that the MKR1310 works fine without any battery attached to it. Did you try long-pressing the reset button while connected to USB ? It should then show up as COM device in the Arduino IDE.
Sorry for the late reply, never got notified of responses ?
So checked again: my MKR1310 does not show up as serial device, you can't upload anything, and double tapping on reset will not do anything, unless you plug in the battery.
Then everything works as it should.
This board is fairly old, got it soon after they replaced the mkr1300.