HVB Energy to Empty

[Riverant]

I suspect this is a variation of the “why is my GOM displaying estimates of 2xx on a 100% charge”. But I charged to 100% yesterday and in my car scanner app, saw that my “HVB Energy to Empty” field said I had 119kwh remaining.

At 100% charge, Shouldn’t this value always be 131kwh in an ER? In theory I should be able to multiply my efficiency by 131 to get my range right?

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[TaxmanHog]

I suspect this is a variation of the “why is my GOM displaying estimates of 2xx on a 100% charge”. But I charged to 100% yesterday and in my car scanner app, saw that my “HVB Energy to Empty” field said I had 119kwh remaining.

At 100% charge, Shouldn’t this value always be 131kwh in an ER? In theory I should be able to multiply my efficiency by 131 to get my range right?

Thermal condition must impact the value.

Run these measurements with the battery preconditioned and at 100%, I suspect it might show better values, if not the computation may include the current air temperature regardless of pack temperature.

 

[Maxx]

Also look at your battery health. It may deduct some there as well.

 

[Riverant]

Battery health is 100% but that’s a true point as well.

It must be temperature where colder weather reduces the amount of available capacity (which makes sense). It then lowers efficiency (which also makes sense). That would further explain why people have questions on the GOM and it seems lower than efficiency alone would suggest.

 

[SpaceEVDriver]

That's exactly right.

People think of a battery as a container of energy, like a volumetric bucket. They imagine the maximum capacity as something they can fill and that is a constant.

The analogy I've been using for cold weather is to think of a the battery as a bucket of water that's been sitting outside in sub-freezing weather. The bucket has a strainer on it so ice can't be poured out. If you fill the bucket with 5 gallons of water, and then immediately pour it out, you expect to get 5 gallons of water back out. But if you let it sit in the cold for an hour, you might expect to get a little less than 5 gallons because a little bit has frozen. If you let it sit for six hours, you might expect to only get 2 gallons of water because the rest is frozen. And it might take some time to get all that water to come out because the ice is making the path more difficult for the water.

A battery is more complex than that, of course. But it's a start toward understanding the fact that the battery isn't a container that holds a specific amount of energy, but is rather a collection of chemical reactions waiting to happen. Cold slows those chemical reactions and you get less energy from the battery. It also slows how quickly you can get energy at all (decreases the maximum power you can pull).

There are other issues too, but these break the analogy above. For example, battery capacity is rated based on a standard discharge rate, typically 100%-0% in one hour. That's the "1C" capacity. If you discharge more slowly, you can get more total energy from the battery. If you discharge more rapidly, you will get less energy. Our 143 kWh batteries--131 kWh of which is made available to us--are rated to deliver 143 kWh at a 1 hour discharge rate (143 kW). Discharge more slowly, say C/5 (5 hours to go from 100% to 0%), and we might be able to pull 150 kWh. I haven't looked at the specs for these cells in a while, so I don't remember the specific ratings. The attached image is an example and it's not specific to our cells.

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