I have basically the same problem with a 1.5Ah pack. All 5 cells have between 3.75 and 3.77V, the output of the pack is only 6.44V and 2 of 4 LEDs are lighting up, but the charger and the tools do not recognise the pack.
I can tell the charger and the tools are ok, since my other packs are working well.
So I guess the allowed charge cycles are reached and Ryobi does not want the planet to survive :(
what a crap!