battery removal thought experiment

I've had a different experience than that based on the nature of the trip. I've driven between California and Nebraska a couple of times, which involves some extended uphill climbs and a few serious pushes over steep summits along I-70. In HV mode, the battery is apparently used to supplement the ICE fairly extensively, because 10s of miles of EV range disappear during the mountain drives.

 

I have not driven the Clarity through the Rocky Mountains. The Tejon Pass (~4100’) in S CA and the Siskiyou Summit (~4300’) in S OR have been the high points.

The decrease in EV range on the ascents has never exceeded single digits. The EV range has always recovered to within 1-2 miles of the original set point after 10-15 minutes of flat or downhill driving. If you’re losing 10+ miles, it may take 30 minutes or more to recover. If the vehicle is stopped and turned off at the summit or before the range has been allowed to recover, a new, lower SOC set point will be established upon start up.

Yes, in HV mode, electricity from both the ICE driven generator and the battery will be required to propel the car uphill at ~70mph. Some EV range will be lost during such high power demand. My experience is that, given sufficient time, EV range/SOC will recover to near the set point after a period of uphill driving.

 

The Colorado passes a little more substantial, with Loveland Pass at about 12,000’ and Vail Pass at about 10,700’. At one point you're doing about eight miles of a near 6% grade, and the ICE leans heavily on the battery for extra HP throughout. (I could, obviously, slow down and that would help reduce the battery use, but that's a different issue.)

Based on my experience on those routes, I think you're not correct about the recovery of EV range back to starting levels as an "intentional" effort on the part of the Clarity. I think in HV mode it simply tries to recover as much energy as it can during downhill runs and the like, but doesn't actively try to return the battery to the original SOC seen at the start of the drive. Because the only way that could really happen would be by using the ICE to charge the battery, essentially entering a covert Charge mode. If that were happening, I'd see the EV miles increasing when I was just cruising, which I don't. Even after burning a lot of EV miles getting over the pass, I still only see the miles going back up if I'm coasting or stopping, just like I would in HV mode on a more typical drive. So even 200 miles/3 hours beyond the pass, no stops, my EV mileage is still near what it was when I originally reached the crest, not when I started the car. The only way I get a substantial number of miles back is if I switch to Charge mode.

 

The passes I’ve driven in the Clarity are also 6-8 miles at 6%, and the decline in EV range while going uphill is 3-5 miles. The main difference being it is an overall lower elevation. I’ve driven the passes you mention, just not in the Clarity.

The ICE does charge the battery in HV. This can be observed by viewing the Power Flow Monitor. Honda uses the term Charge Sustaining mode in describing the operation of the powertrain. The battery does act as a “buffer”, discharging to supply additional power when needed and the ICE generator will recharge the battery when possible.

That said, I believe my understanding of the operation of the powertrain is correct and my experience and observations are consistent with the information provided in documents from Honda.

Your experience, under somewhat similar conditions, appears to be considerably different from mine. This seems to be a fairly common theme with this car and I don’t dispute your experience.