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kWh Used vs SOC Question

kWh Used vs SOC Question

I have a 100D (Dec 18 build). Weekly, I make the same nearly 100 mile trip with no stops and I always charge at home prior to leaving. Typically, at the end of the trip, the trip chart on the dash display shows ~25kWh since last charge, depending on weather conditions, traffic, etc. The %SOC of battery “used” (subtracting arrival SOC from departure SOC) is generally ~30%. So the kWh used is always less than the % battery SOC depletion. Assuming a usable 95 kWh, 30% depletion would be 28.5kWh. I am curious why there is a difference? Perhaps the algorithm the kWh uses in the trip chart differs from SOC algorithm. In any event, the the SOC used is alway greater than the kWh used. Practically speaking it doesn’t really matter but I would like to understand this. Any thoughts?

mbirnie51 | 12. Oktober 2019

@Billp19; your consumption of 25kWh is determined by your average whatt-hours per mile (Wh/m) during the trip times the # of miles traveled. Eg: 300 wh/m times 100 miles traveled will consume 30 kWh. The SOC consumption is a less accurate. I use the wh/m as my target and try and keep it as low as possible. Somewhere about 300 wh/m is a one to one ratio of miles traveled and range consumed. That is for my 2017 build MX75D uncorked vehicle. My life time wh/m is 344 and trending down (I towed a U-Haul for 1000 miles and that killed my life time wh/m). I owned a 2013 MS P85 and my life time wh/m was 317 over 80,000 miles, they are better on consumption than the heavier MX.

Bighorn | 12. Oktober 2019

SOC does not ever degrade whereas kWh capacity will. My 85 kWh battery originally provided 74 kWh and eventually dropped to 65 kWh. That would also be reflected in the shrinking rated range, but would not impact SOC as each % represents fewer Whs. Also FW has the potential to alter the size of buffers and usable battery capacity.