Lithium battery 3.6V 14Ah.

Hi!
I need to deploy MKR GSM 1400 module with 2 x FANSO ER34615M/S STD batteries, if you look them they are 3.6V Lithium with 14.000mAh but my question is, where can I solder cables for powering device?
Will be good using battery port and connect all sensors to VCC?
Maybe using USB as battery powering?
Thanks for you help and regards!

They are LiOn not LiPo so I would not use the battery port.

You have two other choices which are the USB connector as you figured out and the VIN pin.
Take note of the specs of the VIN pin though before committing to your deployment.