There are two status LEDs located on the left of the JST battery connector labeled STAT1 and STAT2. Here is a table of the LED behavior depending on which state the battery charger is in:
STAT1 STAT2 Charge State
ON ON Precharge in progress
ON OFF Fast charge in progress
OFF ON Charge done
OFF OFF Charge suspend (temperature), timer fault, and sleep mode
Is it possible to read the value of each LED in code? or the equivalent (charge state)?
You could solder the R9 and R10 pads that are opposite the LEDs to D-pins of the Particle.
There are apparently also testpads connected to these points somewhere, and you could solder to them instead if they’re big enough.
Thanks, I’ll give that a try.