hmmm, you need to check each cell with a volt meter. On your balancing tab there are 5 wires, one is a ground the other 4 are the posotive for each cell. I'm not 100% about the blinky because I don't have one, but just because all 4 cells don't light up doesn't mean you have a bad cell. It probably means that the other 3 cells are charged a bit more than the 4th cell so the blinky is trying to draw them down to balance the pack. That's how a balancer works by discharging the other cells down to the lowest one. Throw your pack on the chrager and it it reads above 14.8v then you still have 4 good cells. Keep us updated

Jay