Also, note that you can't trust the "energy used" information from the trips meter, because some loads aren't measured by the car.
Huh? I thought all loads are measured on the trip meter while driving anyway. Seems like every load that gets turned on or off, such as HVAC shows up in consumption meter while driving. What loads are not calculated?
How I have been keeping track of battery degradation is by:
1-With a well balanced battery, drive the car to a supercharger that is far enough away to get the car (battery) fully warmed up.
2-Charge the car to 100% at the supercharger until charging stops completely. Reset trip meter.
3-Immediately start driving the car. Drive as steady as possible. No hard acceleration or very high speeds. Flat roads as possible. Freeway driving as much as possible to eliminate start/stops. Try to target 280 to 300 wh/mi.
4-Do not stop driving until you reach your destination with as close to zero rated miles as your comfortable doing. I have been driving down to about 5 rated miles.
5-Take note of kwh extracted from pack (Total Energy on trip meter).
6-Repeat steps 1-5 a year later or whatever time scale you want. Helps to do this when the car is new in order to get a base line battery kwh capability. Take note on how much less kwh you are able to get out of the pack year over year. This is your actual degradation.
Although not completely accurate or totally scientific, it seems to be about the best way to do it. If you don't have a baseline kwh capacity of your pack when new, use someone else's. I believe you can get about 77.9kwh or so out of an 85kwh pack (base on Bjorn's latest run 450mile run). Older rev packs might not be exactly the same.
I have been doing this every year or so on my car. I have about 1.5% pack degradation after 2 years and 50K+ miles on my 60kwh pack. I can still get almost 55kwh out of my pack last time I checked.
The way the OP is calculating pack degradation is just not a very good way of doing it. Using kwh added back into the pack during recharging is a terrible way of calculating pack capacity. The added overhead during charging can very greatly from charge to charge depending on how much HVAC is need to keep the pack cool during charging and other things.