What is your miles/kWh (total average electricity consumption) on the "Drive Monitor 2"

I don't believe 5.46 kWh usable capacity is accurate. Any time I drive from 100% to 0% and divide the trip miles by the miles/kWh on the display I get within a percent or two of 6.0 kWh. That jives with the Kill-A-Watt that tells me a full charge takes 6.6 kWh with the charging system around 90% efficiency.

 

Then my car is lying to me. If I had to choose between the % capacity or the miles/kWh, I'd guess that the miles/kWh is where the inaccuracy lies. Perhaps there is a relationship with the 50-mile limitation on the GOM.

 

Interesting thread. One thing that caught my eye was the lack of expected battery degradation after a year of driving (a tangent, I know). I would expect that the ~33% of unused capacity conceals the initial loss of capacity. I would imagine Toyota would like to manage the battery in such a way that the degradation consumed "reserve" capacity first to give the end user the benefit of 100% usable capacity for as long as possible. A standard LiPO4 battery would require somewhere around 1,200 discharge cycles (using 67% depth of discharge) before degradation reached more than 33%. In my routine that would take 5 - 6 years.

Batteries lose more capacity initially than later on. Data from 400+ users of Teslas suggests that after a loss of 4% in the first ~30,000 miles, they only lost 5% more over the next 120,000 miles. In that case a Prime owner would never feel the degradation over the average time most people own their car.

 

I rather doubt that Toyota would reduce the amount of reserve in order to maintain a consistent amount of useable energy. It seems to me like that would accelerate the degradation of the battery once the car started doing that.

 

An adventurous person could just connect some leads directly to the battery and charge it up to capacity and do a full discharge test at 0.1C.

It would definitely be a judgement call. Do you want to preserve the appearance of zero degradation over the warranty period at the expense of capacity later on, or allow the user to experience degradation earlier in the interest of extending usable battery life even beyond 10 - 15 years? If it were my decision I would opt for the former for warranty and initial owner satisfaction scores.

 

Looks to me like a flat curve for the first 16 months and then a sudden and rapid decline. That would be disconcerting to me because it's the opposite of the expected curve. Even if linear, that would mean the Prime is losing capacity much more rapidly than Teslas.

 

There does seem to be a trend. But like you said, it's a small sample set. I would have the same problem because I rarely use all my charge before I get home. But I do think that I'll start putting an asterisk in front of the charges that are on a depleted battery in the future. I should get one of those tomorrow because I have a 40+ mile trip coming up.

But my other problem with tracking it is that my meter reads in 1 kWh increments once it gets up to 10 kWh or something like that. To be accurate, I'd have to reset it before it gets to that point and add up all the numbers for my total when I get gas every six weeks to three months. That's a LOT of adding! Ideally, I would need two meters.

 

The SOC is only estimated from voltage. I'm not sure the relationship between voltage and capacity is constant as the battery's capacity declines. I'm starting to think the only reliable way to track loss of capacity is to charge the battery to 100% SOC using an independent charger and to discharge it down to 0% independently of the car.

 

Tracking data like this is rather interesting. But I'm not going to obsess over it because all the records in the world won't change how long the battery lasts. A general idea is sufficient for appeasing my curiosity.

And I totally agree, @Salamander_King, about the variation in actual charge state when you get home. That can make a big difference. But if you have lots of data points over several years, you should be able to see how fast it's trending downward. It's just hard to get that many data points unless you outdrive the battery range very often.

 

This is a good task for me since I deplete the battery every single day. I haven't been tracking the amount required to charge, but I can try collecting that info on a regular basis in the interests of science.

 

OK. I kept the MID at 1% until I pulled in the driveway. Then I ran it down with the A/C and rear defroster until it hit 0% and turned the car off to avoid using any of the battery reserved for HV driving. Kill-A-Watt reported 6.39 kWh charge this morning. The charger has a 1.2W parasitic draw, so plugging in when I get home until I leave in the morning leave about 4 hours where it's just sitting there drawing 1.2W, so it's only the difference between 6.385 and 6.390 kWh.

I don't think I need to do this every day, but maybe a couple of times a month to track capacity.

 

It's pretty easy in my situation. The hard part is remembering to get the Kill-A-Watt out and to read it in the morning. Past experience has taught me that leaving one on the outlet for an extended period of time will kill the unit, so I try to use it sparingly.

If 6.3 is with a full HV battery, you've only degraded 1.4%. That's not bad.