Hi there,
you can find the meaning of the four LEDs in the description of the PCB in the shop section 

. It states:
LED 1 means system is ON 
LED 2 means battery is low
LED3 ON + LED4 ON/OFF Means it’s charging 
LED3 OFF LED4 ON means charge is done
I can confirm the first three points. Concerning charging is done, I have to say that the 4th LED never turned on alone on my Raspiboy. Not even after 10h of charging.