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How much of the 20.1kWh is being used? Did they design it to be cautious and worry about the longevity or dipping into more in the future?

I'm a little confused when I see folks talk about switching over to the ICE before the battery runs out as if they are trying to manage the battery somehow.

The Chevrolet Volt has a 16kWh (16.5 in 2013s) battery but uses the middle ~65% (22%-87%) of it ... so about 10.3kWh (10.8kWh in 2013s).

On a post by Rusty using a DashDAQ he determined a finer breakdown of the Volt's battery capacity usage.

http://gm-volt.com/forum/showthread.php?5328-Volt-Diagnostic-Tool&p=91868#post91868
My first results that might be of interest from the DashDAQ OBD scanner, I eyeballed the transitions of each battery bar. The DashDAQ has at least two signals for battery level in the Volt extension driver, one for battery level % and one for the battery gauge %. The gauge turns out to map directly to the battery bars on the display, with each bar ticking off every 10% of the signal range (at least it did for the transactions I happened to watch - staring at the scanner while driving being a bad idea I haven't watched to confirm the entire series).

Here's how it maps between the gauge display and the actual battery SOC (or at least I think the VICM term is SOC).

Code:
Battery Gauge  Gauge %     Actual 16kWh Battery %
10 bars        91%-100%    81%-86.5%
9 bars         81%-90%     74.4%-81%
8 bars         71%-80%     68%-74.4%
7 bars         61%-70%     61.5%-68%
6 bars         51%-60%     55.3%-61.5%
5 bars         41%-50%     48.7%-55.2%
4 bars         31%-40%     42.1%-48.7%
3 bars         21%-30%     35.6%-42.1%
2 bars         11%-20%     29.3%-35.5%
1 bar           1%-10%     22.7%-29.3%
0 bars          0%-1%      20%-22.7%[/SIZE][/FONT]
The ICE comes on around 20% SOC, and the CS (Charge Sustaining) SOC is around 22%. So the ICE runs a bit to bring the SOC back up from 20%ish to 22%ish. This somewhat confirms some of what we've heard about the battery and battery SOC.
 

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Reasons to switch on the ICE before the battery is out:
- you want more power (the Sport stats are at 26M left in the battery)
- you want to drive electric at your destination (ie you drive using the ICE on the highway, but want battery left so that you can drive silent and with no emissions on city streets when you get off the highway)

I always save enough battery to do all city driving electric-only, and use the ICE when ( <26M on the battery && I know I can't make it to a charging station on the remaining battery power ).
 

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How much of the 20.1kWh is being used? Did they design it to be cautious and worry about the longevity or dipping into more in the future?

There are contradictory data about this. Fisker's documentation says that the computer switches on the ICE when the battery hits 15% SOC and maintains that buffer in charge sustaining stealth mode as well as Sport mode. You can see this on the SOC meter on the dashboard that never goes below the last three slices even with the ICE running. Since the battery capacity is 20 KWH, you would expect that with 15% remaining at all times, you would only use 17 KWH to charge the battery from 0 miles (15%) to 50 miles (100%).

However, the EVSE consistently report that it takes 19-21 KWH to charge the battery in that scenario. It is not clear if the 20 KWH represents the 85% of the battery capacity that is available for EV operation and the battery is in fact larger than advertised (not likely), or if 2-3 KWH get used up by other components in the car during charging (more likely). We simply don't know.
 

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Fab et al.,

I believe the actual total capacity of our main batteries is 23 kWh, so 85% would be 19.55 kWh, which is almost exactly what my car accepts when I run the battery down to 0 miles and charge it overnight (19.5 when the car was new, 19.78 currently).
 

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Discussion Starter · #5 ·
drliu said:
Fab et al., I believe the actual total capacity of our main batteries is 23 kWh, so 85% would be 19.55 kWh, which is almost exactly what my car accepts when I run the battery down to 0 miles and charge it overnight (19.5 when the car was new, 19.78 currently).
Datasheet shows 20.1kWh.
http://www.fiskerautomotive.com/Content/pdf/Fisker_Karma_Specs.pdf

2011 Volt uses about ~10.3 kWh but takes ~12.5 kWh to charge it including overhead (conversion losses and cooling system for charger).

Using that same ratio for a rough estimation would imply that the FK uses ~16.29 out of ~20.1 kWh. All very rough. 82% of battery used. I'd find it pretty odd that it would charge the actually 20.1kWh battery SOC to 100% and take it down to 15%. (Recall Volt uses 22%-87% but different batteries obviously).

Would have guess several of you would have discussed your charging numbers and created a spreadsheet to extrapolate if possible.
 

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I routinely charge 19.5-19.9 kWh when the battery is at 0 miles (i.e., the charging station reports that the battery has accepted 19.7 KWh), so the total capacity of the battery seems unlikely to be actually 20.1. Perhaps the USABLE capability (i.e., 85%) is 20.1? I know there is conflicting info on the web about this issue of 20.1 vs 23 vs 18 total vs. usable KWh. Perhaps Fisker engineer could set the record straight here once and for all?
 
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