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Discussion Starter · #1 ·
With very conservative driving, lights off and no other electrical draw aside from the radio, I only get 13.5 to 13.8kWh on the battery until the ICE kicks in. I read in the forum of people getting 14.1 to 14.4. It is a 2017 LT with 22K. It was this way when I bought it at 15K. Should I be concerned? With my driving style and terrain, I can achieve 77 miles in the summer (very little AC usage).

Thank you.
 

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Lithium batteries have a 5% degradation in first while (can't remember time frame) then it levels off after that (assuming no bad cells). Mine was at 96% when bought it and has stayed that way for the last 3+ years. You are also at around 96% (14.4-13.8)/14.4 so if it is relatively stable I would say all's good.
 

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I'm averaging around 13.6 with my 2017, which is consistent with what you are reporting.
 

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13.8 vs 14.1 is virtually the same number (2% difference) essentially in the noise of measurement. 13.8 vs: 14.4 is a 4% difference. maybe outside the noise, but pretty darn close. for a used car, I would not worry.
MikeB
 

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also, kilowatts used does not care how you drive, it will just carry you further if you are conservative...
 

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Same here... 2018 at 42k miles. I've been checking it lately. Once I saw 14.3 kWh. Usually it is at 13.8.
 

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Discussion Starter · #9 ·
Thanks for the reassuring replies and confirming the baseline. Since March when I bought the car, I've been watching and recording drives closely and the battery is stable and predictable.
 

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My 2017 with 38,000 miles only gets about 13.2 useable kW per charge. When checked with the "MyVoltCapacity" android app, it shows that only 15.004 kW of the original 18.4 kW capacity remains (82%). This is apparently at the bottom end of the observed readings for a 2017, so I am not very happy about it. There is a collection of data for different years in this thread: MyVoltCapacity thread.
 

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my 2016 volt that had 14.1 new, now moves all over the place from 13.1 to 14.1
yet the distance that it runs out of battery has not really change much
78,000 miles
 

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also, kilowatts used does not care how you drive, it will just carry you further if you are conservative...
To an extent. Any battery, though, will deliver more power being drained over two and a half hours instead of half an hour.
 

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Good call Peter. Just saying the original post referenced conservative driving, and that does not effect the # of kW-h delivered.
 

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Good call Peter. Just saying the original post referenced conservative driving, and that does not effect the # of kW-h delivered.
That's the thing: IT DOES affect the number of kwh delivered. Not by a lot, maybe 3-5%, and it was far more so in lead acid batteries, but you actually can wring more juice out of a battery drawing it slowly instead of quickly, BECAUSE what marks a battery as "empty" is voltage. Every battery depends on chemical conversion that lags the drawdown, and the rate of drawdown influences the voltage presented, and once you get below the "empty" point you've decided is all you're going to get out of a battery, you're done. In theory-land where everything instantly and without entropy, you've only stopped early because there's still more chemical energy left before the ideally-calculated bottom point is reached, but out here in the slow and heat-death universe, the point at which the engine turns on happens, the draw from the battery lowers, the chemical reactions catch up to the inflowing generated power, and some power that you COULD HAVE TAKEN from the battery remains in it, undelivered, because the voltage got low enough. And every battery system that does more than a simple resistance/short does that because there's a point at which the voltage is too low to be useful and drawing just stops.

edit to add: I dug up what the math is for the lead-acid that modeled out exactly when a system is going to quit early and by how much: Peukert's Law describes it. It doesn't work for Lithium Ion in the same way because a lot of the constants are different, but the effect that Peukert is trying to describe still exists in some form.
 

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Ok, another good point Peter! Sound familiar - draw slow, more A-h available...
 

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To complement what Peter is saying...

The kWh Used shown on the energy usage display is not a reading from a meter, but a calculated net estimate (= grid power used less regen put back into the battery). The Battery State Estimate Algorithm makes "on the fly" SOC estimates as you drive, and can gather additional data to refine the readings when the car is sitting for a while. When you drive far enough to deplete the battery, the number of times your car is paused long enough for the system to gather data to confirm or modify the SOC estimate may have a small impact up or down on that final kWh Used reading (i.e., "power being drained over two and a half hours instead of half an hour").

This may also have an impact when you arrive at the destination... by delaying the recharging instead of immediately starting the recharge, you allow the system time to gather data and refine the "fully depleted" SOC reading BEFORE the recharging starts. This may influence the amount of usable that gets pulled from the wall socket and put into the battery before the computer says the system is at the "full charge" SOC and stops the recharging... makes one wonder if those who use delayed time-of-day charging have more consistent full depletion kWh Used numbers...
 

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The kWh Used shown on the energy usage display is not a reading from a meter, but a calculated net estimate
This is exactly the answer. If the 'best guess' of the computer is wrong, then that is that. I would guess - especially based on miles travelled on battery, that the usage pattern isn't well modelled in the algorithm and total charge used is just slightly mis-calculated.

-Charlie
 

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Something else to keep in mind: the Volt is an extended range electric car. You can’t just keep driving until the fuel tank is empty. The traction battery is also being used when the car’s range is being extended (i.e., when the engine is running). That means the Volt can’t use ALL of the usable battery power for Electric Mode driving. Some needs to be reserved at the low end for extending the range.

The Volts have been programmed to use a fixed portion of the full capacity for Electric Mode driving (Electric Miles, kWh Used). You charge from the wall until the "full charge" SOC level is reached, and there’s a small amount of accessible space above that so the regenerative brakes will work with a full charge. You drive, depleting the charge, until the bottom of the Electric Mode window is reached, and then the car transitions from charge depleting to charge sustaining mode. The battery buffer from that SOC point to the "hard floor" point (my understanding, ~5% of the battery’s full capacity) is the portion of the battery used when extending the range.

Wikipedia articles indicate that Electric Mode window is ~76% of full battery capacity for the Gen 2 Volts, and 65% of full battery capacity for the Gen 1 Volts. Note that as the battery loses capacity over time, so does the kWh Used in the "full charge" window (e.g., 76% of a Gen 2 Volt 18.4 kWh battery = ~14.0 kWh, but 76% of a battery that has lost 2% of its original capacity = ~13.7 kWh).

Now consider what the system must prepare to do while the car is moving down the road and the SOC is dropping to the "transition to gas" point. At some point, the engine must be started so the smaller motor MGA can be cranked as a generator and/or the engine used for propulsion. MGA draws power from the traction battery to start the engine, but if you start the engine while the accounting is still in Electric Mode, that "engine starting power consumption" will need to be recorded as kWh Used during Electric Mode operation... so ideally you will transition to gas before you draw power to "start the engine."

Not so much of a problem if you are moving at a slow speed ("lead from the battery, and follow from the generator"), but what if you are racing at high speed down the highway (or up a mountain road or the a/c or heat is blasting to keep the cabin cold/hot) and the SOC is dropping like a stone? At what point does the programming determine it is prudent to start the engine NOW so the generator is up and running in time to keep the SOC above the point that would trigger a Propulsion Power Reduced episode? Might you need to shave a bit off the bottom of the Electric Mode window to avoid a PPR? Thus some small variation in the kWh Used may be related to the driving conditions being experienced at the time the transition to gas is made.
 

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Not so much of a problem if you are moving at a slow speed ("lead from the battery, and follow from the generator"), but what if you are racing at high speed down the highway (or up a mountain road or the a/c or heat is blasting to keep the cabin cold/hot) and the SOC is dropping like a stone? At what point does the programming determine it is prudent to start the engine NOW so the generator is up and running in time to keep the SOC above the point that would trigger a Propulsion Power Reduced episode? Might you need to shave a bit off the bottom of the Electric Mode window to avoid a PPR? Thus some small variation in the kWh Used may be related to the driving conditions being experienced at the time the transition to gas is made.
Plus, there's a period (which feels like FOREVER but is probably actually only 20-30 seconds, or a couple hundred watt-hours at highway speed) from starting the engine (which also takes energy) until it's warmed a little bit and is ready to work at full. You can hear when it starts working even over road noise and wind. But that means that the SOC is in a non-trivial amount of energy debt BELOW the point at which it switched to Charge Sustain, which is the bottom of the range of charge that CS operates within. It's the LOWEST state of charge that a car being operated under normal conditions can possibly be expected without something being Seriously Wrong and popping a PPR.
 

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My average is 13.2 KWH on a 2017 with just over 60,000 miles. I have seen from 12.8 to 13.8 KWH within the last couple of months. The capacity suddenly dropped from an average 14.1 about a year ago (~52,000 miles) and has stayed at the current average level of 13.2 since then. Average range is 59 at moderate speeds - only about 10 - 15% highway driving.
 
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