It’s possible to power SARA R412M module with non-rechargeable batteries like ER1850M ones? Of course without using solar power
The second question if the first one is true it is safe to have connected battery like those mentioned and connect the board to usb?
You can use any powersource if the range is between 3.3v and 5.5v
There is a solder jumper you can remove to disable the chargecontroller.
When the solder jumper is removed you can have the non chargeable battery and USB connected at the same time.