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Discussion Starter · #1 ·
Over the past couple of months I've noticed that when my PHEV stops charging I only have 25 miles of range on the display. The PHEV battery information menu shows 99% charge, but I'm not sure that's new, it might always have said that. I think it might be an early indication of battery degradation.

Here's a chart of my ChargePoint sessions since 2019 which accounts for the vast majority of my plug-ins. I restricted the chart to days with at least 5 kWh and less than 10 kWh in a crude attempt to capture just full charges. It's clear from the chart that I still have some partials and some days with more than one, but there is a clear trend. The overall trend is -.0002 kWh / day which works out to a .2kWh or 2.5% loss of capacity over the 3+ years of the dataset. In addition, though it's hard to be sure since there are gaps in the data, it looks like prior to 2020 there was little to no trend but it starts dropping after that. If I calculate the trend after 2019 it works out to -.0004 kWh / day, a significant increase.
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Some data for the 2018 PHEV Niro from EV Battery Health - What 6,000 Batteries Tell Us | Geotab shows a similar trend. Flat for a while, then dropping off steadily. Sorry for the crap image quality, I had to cut and paste the image from the web page.

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If you squint you can see that at ~2 years of age the plug-in Niro has lost ~5% of its capacity. Mine is significantly better than that, having only lost 2.5% in over 4 years but that could be down to my driving habits.

Have any other long term PHEV owners noticed a similar loss of battery capacity? Obviously, this is to be expected as the pack ages and accumulates more charge / discharge cycles.
 

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Discussion Starter · #4 ·
That article appears specific to EV batteries. You can't compare the EV and PHEV in that way. Two completely different systems, different levels of power draw and charging. That said, mine would always show 100% charge after a complete charging session, but as soon as I pulled out of the driveway (it's uphill) it would drop to 99% and using regen it would never reach 100. Only connected to my JuiceBox or some other Level 2 EVSE would bring the display to 100%.
While the article focused on BEVs, the plot I posted was specifically from the 2018 Niro PHEV so it's literally apples to apples (🍎 to 🍏 at least 😁). I'm aware of the differences between BEVs and PHEVs but regardless, any electric vehicle will experience some degradation in its battery capacity over time, HEVs significantly less due to their use case and likely much less noticeable due to the fact they don't really operate in pure EV mode for very long periods.

Like you I saw no change in estimated range over the first 3+ years of ownership, this is a very recent thing. Also, as @Johnxyz mentioned, I have in the past seen occasional charges stopping at 25 miles of range, but this trend is very consistent, regardless of whether the battery was completely discharged or not, whether the charger used was Level 1 or 2, winter vs summer, etc.

Looking at my personal charging data it seems likely that there is some slow decline in capacity. Is it significant? I dunno, the data is kinda sparse and I'm picking full charge cycles in a very rough way so I'm not willing to bet my life on it but there is definitely a trend evident in the plot. If I'm right about the battery losing ~2.5% capacity that works out to ~25.4 miles of range vs 26 when new. If the ECU is computing estimated range based on capacity and simply rounding the result to the nearest whole number then it makes sense that I've just started seeing this in the last couple of months. Sure, there are a couple of "ifs" in there, but the logic seems sound. Based on the data, I would predict that my estimated range will drop to 24 in about 2 more years. Would I wager my paycheck on that prediction? Nah, but I might put $20 on it. We'll just have to wait and see.

It would be interesting to see if anyone else has long term charging data that shows a similar decline.
 
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