Hi BravoPilot, welcome.
I suggest you to check battery voltage of each cell using a multimeter on Vcc 0,01 scale. Then report here results.
The blue blinking light on the charger could be caused by cells unbalanced on the battery, and remain in memory until a good battery is plugged.
It could also be a fault in the charger, or in the battery.
I would suggest checking the spring loaded pins in the charger to make sure they are all contacting the battery. Check the flat bladed Deans pins to make sure they have the thin curved spring metal portion that provides good contact with the battery.
As for the batteries follow @Pier2162 suggestion to measure the cell voltages and report the results. Instructions are attached to this post.