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I can actually answer the battery question with relative confidence.

Three very important numbers. (I don't have access to the battery pack information, so doing this as a general statement)

Soft Cell Cutoff- This is the lowest voltage that the battery can discharge rated amperage, and is considered effective at.
Nominal Voltage- The natural homeostasis of a battery.
Maximum Voltage- The highest safe charged level for a battery.

When a battery is below nominal voltage, it actually wants to charge. This is why the battery seems to charge fastest from 2-6 bars.
Once a battery hits nominal voltage, it'll still accept a charge, but is less willing to do so.
As a battery nears maximum charge, it's more resistant to charging. Also as it nears this, the rate at which it'll charge decreases. As part of the charging system, it'll essentially trickle charge at this point.

Example. Sony VTC5 18650 battery.

Hard Cell cutoff 2.7v, soft cell cut off 3.2v Nominal Voltage 3.7v. Fully Charged 4.2v
If I throw a battery on the charger at let's say 2.7v and another at 3.2v. They will both charge to 3.7v on 1 amp of current in less than 2 hours. Once at 3.7 the charger will stay at 1 amp of charge until 4.0 volts. This will take approximately 2 more hours. Above 4.0v to maximize the lifespan of the battery, the charger will start dropping charging current. It'll take approximately 2 more hours to achieve that last .2 volt charge.

You could charge the battery faster, and force more charging current, at the expense of battery lifespan. Also it'll generate a lot more heat.
I had a feeling whatever algorithm Honda set for the Insight will always put priority on battery lifespan. Your explanation helps to explain the weird logic behind the battery sometimes not charging or being used. I'm guessing the car also has a hidden battery reserve that we don't see even when the battery indicator shows full charge/low charge similar to how the gas tank has a hidden reserve even when the display audio tablet is showing 0 miles left in the tank.
 

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I had a feeling whatever algorithm Honda set for the Insight will always put priority on battery lifespan. Your explanation helps to explain the weird logic behind the battery sometimes not charging or being used. I'm guessing the car also has a hidden battery reserve that we don't see even when the battery indicator shows full charge/low charge similar to how the gas tank has a hidden reserve even when the display audio tablet is showing 0 miles left in the tank.
I tend to agree on hidden reserves or limits. If you had to cover the battery under a 10 year warranty, you would probably do everything possible to prolong the life span by being gentle on the battery.
@Wifey'sInsight

Sounds plausible. It used to keep charging in cooler weather. Now that it's warmer, it changed. I am thinking "heat" plays a role in this equation. 60 degrees seems to be the sweet spot for charging.

Phil
 

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I tend to agree on hidden reserves or limits. If you had to cover the battery under a 10 year warranty, you would probably do everything possible to prolong the life span by being gentle on the battery.

@Wifey'sInsight

Sounds plausible. It used to keep charging in cooler weather. Now that it's warmer, it changed. I am thinking "heat" plays a role in this equation. 60 degrees seems to be the sweet spot for charging.

Phil
Yes, heat plays a major role in batteries, including charging and discharge characteristics.

Too cold, and the chemicals don't want to move, although it accepts electricity quicker. (Doesn't necessarily charge faster, more energy is converted into thermal energy), although with Atkinson cycle and cabin heat, the ICE will run more.

Too Hot= more natural resistance, and shorter battery life if operated in higher ambient temperatures. Ideally, and I believe that Honda addresses this. The in cabin temperature helps to cool the battery pack via the vents for the battery area.

Most batteries charge quickest around the middle of their operating temperature range.
 

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Given it’s relatively small size compared to other hybrids and the large number of times that the battery cycles (charges and discharges) during a short drive, I wonder if this is going to affect the battery’s lifespan, which will in turn degrade MPGs over time. Just think if your iPhone battery discharged and recharged several times a day. Any thoughts? I know there’s an 8 year warranty, but that’s little consolation if MPGs take a hit much sooner than when they’ll replace the battery (i.e., what they consider normal degradation).
 

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Discussion Starter #5 (Edited)
Given it’s relatively small size compared to other hybrids and the large number of times that the battery cycles (charges and discharges) during a short drive, I wonder if this is going to affect the battery’s lifespan, which will in turn degrade MPGs over time. Just think if your iPhone battery discharged and recharged several times a day. Any thoughts? I know there’s an 8 year warranty, but that’s little consolation if MPGs take a hit much sooner than when they’ll replace the battery (i.e., what they consider normal degradation).
The battery in the mobile phone is consumer grade, optimized for maximum runtime at low cost. the EV battery, on the other hand, is made to industry standards with longevity in mind. The dissimilarities do not stop there and a key difference is how the energy is dispensed.

A mobile phone gets charged at the end of a day and the stored energy can be fully utilized until the battery goes empty. In other words, the user has full access to the stored energy. When the battery is new, the phone provides good runtimes but this decreases with use. In this full cycle mode, Li-ion delivers about 500 cycles. The user adjusts to the decreasing runtime, and being a consumer product, the end of battery life often corresponds with a broken screen or the introduction of a new model. Built-in obsolescence serves well for device manufacturers and retailers.

The EV battery also ages and the capacity fades, but the EV manufacturer must guarantee the battery for eight years. This is done by oversizing the battery. When the battery is new, only about half of the available energy is utilized. This is done by charging the pack to only 80% instead of a full charge, and discharging to 30% when the available driving range is spent. As the battery fades, more of the battery storage is demanded. The driving range stays constant but unknown to the driver, the battery is gradually charged to a higher level and discharged deeper to compensate for the fade.

Once the battery capacity has dropped to 80%, the oversize protection is consumed and the battery maintenance system (BMS) applies a full charge and discharge. This exposes the EV battery to a similar stress level of a mobile phone and the driver begins noticing reduced driving range. Battery replacement may become necessary but the cost will be steep and higher than a combustion engine. https://batteryuniversity.com/learn/article/why_mobile_phone_batteries_do_not_last_as_long_as_an_ev_battery
The difference is in the usage time. Suppose you drove 100,000 miles at an average 40 mph. That makes 2500 hours of effective driving, or 104 days. Compare this is with a phone which is used day, in day out, mostly being daily charged, for a couple of years. If you compare 104 days with, say 1000 days (for less than 3 years life span), things become easier to explain. An don’t forget that in a hybrid, the battery is not used all the time!
I found an article comparing an iPhone battery and EV battery. Also added a side comment I found that differentiates a hybrid battery from a full EV battery.


With iOS 13, Apple also added a 80% battery optimization option, in the settings app.
 

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I found an article comparing an iPhone battery and EV battery. Also added a side comment I found that differentiates a hybrid battery from a full EV battery.
Thanks for the info! The EV battery comparison is interesting, but I wonder how well it applies to the Insight battery, which has a much greater cycle rate (many more charge/discharge cycles compared to a pure EV). Also, the last quoted section says to remember that a Hybrid battery isn't used all the time. True, but isn't the only time the Insight battery is not being used (discharged) is when you're in the green (coasting or braking)? There's really no steady state (not being charged or discharged) for the Insight battery, except when the car is off, right? Isn't this a bit different from some Hybrid models where the gas engine is the sole propulsion system (no electric motor assist and therefore no battery drain) at times?
 

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Discussion Starter #7 (Edited)
Thanks for the info! The EV battery comparison is interesting, but I wonder how well it applies to the Insight battery, which has a much greater cycle rate (many more charge/discharge cycles compared to a pure EV). Also, the last quoted section says to remember that a Hybrid battery isn't used all the time. True, but isn't the only time the Insight battery is not being used (discharged) is when you're in the green (coasting or braking)? There's really no steady state (not being charged or discharged) for the Insight battery, except when the car is off, right? Isn't this a bit different from some Hybrid models where the gas engine is the sole propulsion system (no electric motor assist and therefore no battery drain) at times?
I'm not really an expert in battery chemistry and couldn't find any info on battery life for a series hybrid. Maybe trying to find a 2014 accord hybrid owner will help give us an idea on battery life? The 2014 accord hybrid was the 1st car to use the new dual motor hybrid system. The 2017 accord hybrid & Clarity use the 2nd generation. 2018+Accord Hybrid & 2019+Insight are currently on the 3rd generation.

https://www.hondarandd.jp/point_search_result.php?mode=search&keyword=lithium&imageField.x=0&imageField.y=0&category_id=
^Research papers from Honda on lithium batteries(requires creating a free account to download). Too technical for me to understand but you might find something in there that's useful.


Edit: Just found this 14 Accord Hybrid owner posting on reddit saying he's pushing 900 miles per tank(15.8 gallon fuel tank). It was just posted 20 days ago. https://www.reddit.com/r/HondaAccord/comments/cyhetv/pushing_to_900_miles_per_tank_on_my_2014_accord/
 

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I'm not really an expert in battery chemistry and couldn't find any info on battery life for a series hybrid. Maybe trying to find a 2014 accord hybrid owner will help give us an idea on battery life? The 2014 accord hybrid was the 1st car to use the new dual motor hybrid system. The 2017 accord hybrid & Clarity use the 2nd generation. 2018+Accord Hybrid & 2019+Insight are currently on the 3rd generation.

https://www.hondarandd.jp/point_search_result.php?mode=search&keyword=lithium&imageField.x=0&imageField.y=0&category_id=
^Research papers from Honda on lithium batteries(requires creating a free account to download). Too technical for me to understand but you might find something in there that's useful.


Edit: Just found this 14 Accord Hybrid owner posting on reddit saying he's pushing 900 miles per tank(15.8 gallon fuel tank). It was just posted 20 days ago. https://www.reddit.com/r/HondaAccord/comments/cyhetv/pushing_to_900_miles_per_tank_on_my_2014_accord/
It's hard to be impressed when she's only getting mid-50s mpg average with a 15.8 gallon tank. Some of us can get near/over 700 miles with the Insight's 10.6 gallon tank.
 

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It's hard to be impressed when she's only getting mid-50s mpg average with a 15.8 gallon tank. Some of us can get near/over 700 miles with the Insight's 10.6 gallon tank.
Yes, I know but I posted that as an example to give @CosmicBlue an idea of what we can expect from our HV battery. Since that redditer is getting above EPA numbers even after 5 years on the 1st gen dual motor hybrid system. Our 3rd gen dual motor hybrid system should be even more advanced in prolonging our HV battery.
 

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Yes, I know but I posted that as an example to give @CosmicBlue an idea of what we can expect from our HV battery. Since that redditer is getting above EPA numbers even after 5 years on the 1st gen dual motor hybrid system. Our 3rd gen dual motor hybrid system should be even more advanced in prolonging our HV battery.
Maybe also looking at fuelly trend/results for Accord Hybrids over the past 5 years will also provide insight on battery life/cycles. If average mpg results drop over time (if 1st gen was 5 years ago) for all cars, we could relate it to battery degradation as most likely cause (?). It might also give a sense for how well the HV battery is doing 5 years into the 8 year warranty.
 
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