Most obvious first...Are you describing the peak charging voltage dissipating down to the nominal running voltage?
Most of a cells capacity is delivered at nominal voltage, so fully charged pack showing peak charging voltage will have a tendency to sag down to nominal voltage under load.
So this has been happening all along since 2009? Or is this a new condition? "Been using since 2009. Always the same results" contradicts "next run is great as the day I bought them".
Yeah, full, detailed system hardware info and battery charging/discharging history is needed for a less general response.