not very accurate (on 13,55volts only red led is light, on 13,50 volts - nothing, this mean 0% for 3,37volts per cell which is too early, the battery has at least 30-40% until full discharge at 2,75 volts for each cell) , the model of micro controller is wiped out so you cant find datasheet and correct resistors for more accurate measuring
All is OK! Recommend!