Notify when temp is too hot for charging

[Stefal]

Subject of the issue

When you can't charge your Facet/Express battery, you can't know if it's a temp issue or something else.

Expected behavior

Perhaps the Facet/Express could display a warning when the temp is too hot.

• Blinking charge led
• Alert on the lcd
• Message on the serial port stream
• All of them ?

[nseidle]

Oh this is a good idea, but one that may be harder to implement than at first glance.

The charger IC uses its own thermistor to detect when to cut off charging:

In the current hardware we don't have access to this temp value, or to the charger IC status (other than the charger LED).

Ideally we would have access to STAT1 and STAT2. Looks like it goes LOW when charging is complete. If STAT1 goes HiZ, and STAT2 is low, then we know charging is complete. If STAT1 goes HiZ and STAT2 goes HiZ, we know we have temp fault. But as I mentioned, that's a hardware rev (not impossible).

We could check the internal temp sensors of the ESP32 and the ZED but they will likely not be useful as they themselves get quite hot and not good for ambient.

The fuel gauge IC MAX17048 has temp compensation but no external temp data.

Hmm, can't think of a better solution than board rev's. Sorry! We'll roll the STAT1/STAT2 rev into the next gen of boards.