FalconFour's observations match my experience over the years. The 2011 lost regeneration and quick charge rate as original battery deteriorated. The LBC (or BMS) limits maximum voltage during charging and regeneration so current allowed (and charging power) goes down as internal resistance increases. I first noticed loss of regeneration when weather cooled in the fall of 2012 after losing 2 bars during the summer of 2012. I eventually noticed that QC charge rate really tapered off above about 60% SOC. Regeneration and QC returned to normal when battery was replaced in fall of 2013 and started to drop when weather cooled in fall 2014 (replacement battery was down to 11 bars by the time of the crash). The 2015 has much lower internal resistance and still has maximum regeneration at high SOC. The SOH percentage seems to follow AHr and GID numbers while Hx deviates from those so I also believe Hx is a representation of internal resistance (or conductance). The 2015 has lower internal resistance (measured by observing pack voltage drop under full acceleration at low SOC) after 20 months and 29,000 miles than the replacement battery in the 2011 when it was nearly new. Therefore the Hx numbers cannot be directly compared between the old battery type and the 'lizard' battery because they both start at about 100% but 100% represents a lower internal resistance on the 2015 than on the 2011.
Gerry
Gerry