An explanation I've read is that health represents the battery's internal resistance - but not much to explain what that represents. The internal resistance is how much the voltage drops under load - how much effort the battery has to put forth to deliver the amount of power being consumed. This is what makes or breaks a battery, and why lithium has such a huge advantage over lead and earlier batteries: it has a very low internal resistance. As this resistance rises, health gets lower. I'd imagine the Leaf's computer uses this information to protect the battery as much as it can, by setting limits as needed regarding regen and acceleration.
In other words, health is actually very important. This explanation of internal resistance goes in line with all the trends I'd seen in posts I've read so far, and my own car's experience. It could spell an early decay for a strained battery. It seems very much dependent on how much strain is put on the battery during its use.
From here; http://mynissanleaf.com/viewtopic.php?f ... 50#p319070
Getting close to an understanding/definition. Actual internal resistance calculations (delta V/ delta I) should have been done with a varying
battery temperature. Hx highly correlates with the ratio of degraded battery conductance to the new battery conductance, just as SOH
relates the degraded Ahrs to the new battery Ahrs.
#1 Leaf SL MY 9/13: 76K miles, 47 Ahrs, 5.0 miles/kWh (average), Hx=70, SOH=78, L2 - 100% > 1000, temp < 95F, (DOD) > 20 Ahrs
#2 Leaf SL MY 12/18: 10.3K miles, SOH 109Ahrs/115Ahrs, 5.2 miles/kWh (average), DOD > 20%, temp < 105F