sslupsky:
The MKRWAN 1310 now includes a secondary lithium battery charger circuit. Secondary lithium batteries are "rechargeable". Secondary batteries are commonly referred to as "Lithium Ion" or "Lithium Polymer".Lithium primary cells, such as Lithium Thionyl chloride batteries, are not rechargeable. Primary batteries are sometimes referred to as "Lithium Metal" batteries.
If you attach a lithium primary cell to the charging port of the MKRWAN 1310 and the MKRWAN is connected to an external power source such as USB or a power adapter, the battery could catch fire or explode.
To use a lithium primary cell with the MKRWAN 1310, you should use a regulator to regulate the battery voltage to the voltage level of the MKRWAN. Typically, this is 3.3V. (I have operated the MKRWAN at 2.7V). The regulated voltage can be applied to the +3.3V input of the MKRWAN.
Just an idea...
When USB is connected to the MKR1310 there are 5V on the 5V-pin present, right? Then should it be possible to switch a normal closed relay with it. And over this relay is the Lithium battery connected. At the moment you connecting USB the relay will open and break the battery connection... Provided the 5Vpin can supply enough current to switch the relay... is there 10mA possibly on this 5V outpin?!?
... or with a diode in front of the + battery ...