What does a slow flashing (1 per second) charge LED flash mean? I have seen in a few times now, and when I unplug and plug in again it goes solid again and finishes charging.
Charging suspended due to input over-voltage, temperature sensor fault (should not occur on the Electron since it doesn’t include the battery thermistor), charge timer fault, or system over-voltage, as generated by the BQ24195 charge controller.
It also possible for the settings stored in the BQ24195 to get weird values that might cause that to happen. Some of the values are stored in non-volatile memory so removing power won’t reset them.
Of course a defective battery could also cause this (typically a charge timer fault) as well.