What's your battery capacity???

[user 667]

I have a 2013 Ford Focus Electric that I want to replace with a Bolt EV when the Bolt EV becomes available in my state. On the Focus EV forum we figured out how to measure the complete usable battery capacity. We charge our cars completely, reset the trip meter which has a kWh reading, then drain the battery including letting the car sit in the driveway with the heater on until the "Stop Safely Now" light comes on.

The maximum usable kWh value could then be read directly off the trip meter. The highest measured usable battery capacity reported for the Focus Electric was 20.4 kWh out of a rated capacity of 23 kWh. This measurement is important for an EV because not only does it give you a very good indication of how much battery capacity you have available on the road without depending on the Guess-O-Meter but it also gives you a baseline that you can compare year to year in evaluating battery degradation.

I know that the Bolt has a rated battery capacity of 60 kWh but what is the usable measured battery capacity of a brand new Bolt? Has anybody even tried to measure the usable battery capacity of a Bolt EV yet? Have the Bolt owners figured out how to safely measure the full usable battery capacity?

 

[SparkE]

Not surprisingly, the topic has come up before. Search this forum if you want the details as to how it was calculated, but the usable capacity is 60 kWh.

 

[user 667]

Not surprisingly, the topic has come up before. Search this forum if you want the details as to how it was calculated, but the usable capacity is 60 kWh.

Well that post was useless. I check the forum on battery capacity tests BEFORE I posted and found nothing but a bunch of guesstaments. If you know where the thread is that shows REAL usable battery capacity test information please provide thread name and sub-forum name.

Usable capacity IS NOT 60 kWh. I don't think any EV ever made has/had the same usable measurable battery capacity as the rated battery capacity. The usable measurable battery capacity is very important for every electric vehicle and should be measured at least once a year for every EV.

 

[Zoomit]

I don't think GM has ever said 60kWh was a "rated" capacity. Please provide a source that indicates 60 kWh is the total energy capacity of the battery.

 

[user 667]

I don't think GM has ever said 60kWh was a "rated" capacity. Please provide a source that indicates 60 kWh is the total energy capacity of the battery.

The Bolt website specifically says, "the battery pack has an energy capacity of 60 kWh". Electric vehicle manufactures always list the rated battery capacity and never list the usable battery capacity. There is always some unusable battery capacity held back primarily for battery pack protection and we won't have any idea how much is held back until we get some real world usable battery capacity tests.

 

[michael]

BoltWannabe is correct in describing the way we on the Focus board check usable capacity and, incidentally, watch that capacity drop over the years.

The issue of Bolt battery size is discussed at length in this thread

http://gm-volt.com/forum/showthread.php?274050-Does-Bolt-EV-have-a-battery-buffer-like-in-the-Volt

It appears, based on reports from test drives, that the usable capacity of a brand new battery is right around 60 kWh, and that the rated "full capacity" is only slightly higher. Many people suggest around 64 kWh.

This high utilization is dramatically different than in the Volt and of 80 mile class cars, but it is consistent with Tesla practice. A large battery does not need to work as hard as a small battery (fewer cycles over the same distance) and also can be made to operate over a narrower range of SOC than the maximum made available.

It is reasonable for GM to have allowed a wide range of SOC not only because it is safe for the battery, but also so that they could a large range. Had they, for example, limited the SOC to the 90%-8% range of a Focus, they would likely have fallen short of 200 mile rated range. Better to make almost all the battery's capacity available, provide a warranty that allows substantial fade over time and miles, and allow the user to preserve the battery by managing the SOC in daily use. This also allows the user to get the maximum miles when needed.

It does not harm a lithium battery to be taken to 0% SOC occasionally. Bottom reserve is provided so that there is no risk of the battery over depleting and bricking. Why should a car stop in the middle of the night with 8% SOC remaining because they worry about someone leaving a discharged car sitting for months? Fully discharged is not the same as dangerously over discharged.

GM's approach, which I agree with, seems to have been: Let them charge it way up and discharge it way down if they want. We warrant that if treated in this manner the battery will still have 60% of its initial capacity after a certain time and number of cycles. In the meanwhile, if you want to drive 238 miles in one go, you can. At least when the car is new.

 

[Zoomit]

I don't think GM has ever said 60kWh was a "rated" capacity. Please provide a source that indicates 60 kWh is the total energy capacity of the battery.

The Bolt website specifically says, "the battery pack has an energy capacity of 60 kWh". Electric vehicle manufactures always list the rated battery capacity and never list the usable battery capacity. There is always some unusable battery capacity held back primarily for battery pack protection and we won't have any idea how much is held back until we get some real world usable battery capacity tests.

EV manufacturers do a variety of things with regard to advertising pack capacity. Here's a very long thread on TMC about Tesla owner's coming to the realization that the stated "75kWh" battery doesn't have either 75kWh total capacity or 75kWh usable capacity.
https://teslamotorsclub.com/tmc/thr...-about-specifications-60-to-75-upgrade.82265/

Another example is the Kia Soul EV, which is advertised as 27kWh: http://www.kia.com/us/en/vehicle/soul-ev/2016/features
The INL testing indicates that is the usable capacity. The tested pack capacity is 32.5 kWh.
https://avt.inl.gov/sites/default/files/pdf/fsev/fact2015kiasoulev.pdf

 

[sgt1372]

The issue of Bolt battery size is discussed at length in this thread

http://gm-volt.com/forum/showthread.php?274050-Does-Bolt-EV-have-a-battery-buffer-like-in-the-Volt

Thanks for this link. I was pondering whether I should be fully charging my Bolt after every use (as I have been doing the past couple of days).

Something told me that I shouldn't be doing this and then I read various articles online that state (in fact) that one shouldn't always fully charge an EV because it increases the degradation of the battery over time.

The consensus in the thread above is that we should engage the Hilltop Reserve feature so that the car is not charged over 90%. I was also thinking that this was something I should and it was good to get independent confirmation of that.

The only caveat, based on my reading, is that one should occasionally charge the battery fully in order to "balance out" the cells. I'm not clear how often this should be done but I'm thinking at least once a month should suffice.

Another caveat is that one should not leave the car in a 100% SOC for too long and it is best top off the charge (from 80-90% charge to 100%) just before you plan to drive the car, which can be managed w/the programming features of the Bolt.

A lot of stuff to remember. Fortunately, I leased my Bolt and if I f**k it up, it will be someone else's problem not mine. I will however make a sincere effort to not totally trash the battery before lease end.

 

[boltage]

Preserving the battery capacity should be easier to do in a long range EV than in a short range EV. In a short range EV, you are more likely to end up at very low levels of charge, are more likely to need to charge it completely full to ensure having enough for a day's drive, and are more likely to want to top it up at every opportunity. With a long range EV, you may not have to do these things, so you may be able to keep the state of charge in the 20-80% range more.