I’ve had a 2023 Bolt for three months. Love it! I know there are lots of questions and responses about charging, but hopefully by this time the 80 vs 100% question has been answered. Here is my question: I currently charge to 80% although all my charging takes place at home using my L2 charger. I read that charging to 80% is the norm when charging at a public fast charger and understand why. However, the same article insinuated that it’s not necessary when charging at home where charging time is not an issue. That makes sense to me, however, if I decide to charge to 100% is the cost of electricity disproportionately higher when charging the last 10-20% because it takes longer to charge that last 10-20%? It makes sense that it would, so why spend more to charge that last 10-20% if I get enough range to meet my driving range needs at 80%? Am I looking at this correctly? Opinions?
Charge to 80 or 100% at Home?
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That would depend on your utility rates, and when you charge. We live out in the country with a coop electric utility. We have a flat rate for electricity 24/7/365.
Charging the last 20% doesn't use more energy. The charging rate is actually slowed down.
Typing only with generic Lithium Ion battery knowledge, and not knowing the specifics of our car, I can state that it's typically healthier for the battery if it's not charged to 100% (or allowed to get below 20%.)
However, there might already be buffers built into the car (meaning there's still unused battery capacity even when the car reports a 100% charge) or the specific chemistry of the battery might make the above statement untrue. I'm not willing to guess wrongly.
Typing only with generic Lithium Ion battery knowledge, and not knowing the specifics of our car, I can state that it's typically healthier for the battery if it's not charged to 100% (or allowed to get below 20%.)
However, there might already be buffers built into the car (meaning there's still unused battery capacity even when the car reports a 100% charge) or the specific chemistry of the battery might make the above statement untrue. I'm not willing to guess wrongly.
According to an OEM battery designer I know, all lithium ion batteries, in current use, are less stressed when used in the middle of their voltage range.
Shouldnt be more electricity, but we recommend charging to 80% to hopefully preserve more of the battery over the long term. Studies have shown that li ion batteries retain more of their capacity when discharged between ~30-80% vs 50-100% (same 50% usage, but 30 to 80 retained more of its capacity throughout the battery cycle test).
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L2 charging doesn't follow a curve like DCFC, it will maintain constant charging speed up to around 100%, maybe tailing off slightly at 98-99% for cell balancing. So, utility costs shouldn't be a consideration. The logic is, DCFC generates heat from higher current (amps) and needs to slow the pace. At 90% or more, the charging speed drops to near the speed of AC charging. So with AC charging, you never have to slow down until you get to the cell balancing phase.
On lower powered DCFC, the charging doesn't typically slow until higher state of charge. The following chart applies to the original 60kWh packs in older Bolts, but the concept is similar with newer packs, but follows a curve rather than step downs. Notice the higher SOC at lower kW charging speeds before the step downs occur.
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When charged > 90%, regen will be limited for the first part of your journey.
Lots of articles advise not charging to 100%, that may or may not be as true for EVs as for laptops and other devices that lack thermal conditioning, but why risk it? If 80% is adequate for daily needs, use it. When planning a longer trip, charge to 100%, and if possible target finishing the charge as close to departure time as possible to avoid sitting at 100% for lengthy periods.
There may be headroom at the top, above 100%. But it is not accessible, and some who have dug in deep claim Bolt has very little room past 100%. It isn't like volume measurements, it is a voltage question. Pack voltages are kept within "safe" ranges so as to not stress cells.
The 80% suggestion for public charging is as much about slow DCFC past 80% as it is opening access for others. On trips, your strategy plays out better by making more stops and keeping SOC in the faster part of the charging curve. Charging from 80-100% on DCFC probably takes more time than 20-60% in most cases, so you will make better time avoiding >80% in most cases.
On lower powered DCFC, the charging doesn't typically slow until higher state of charge. The following chart applies to the original 60kWh packs in older Bolts, but the concept is similar with newer packs, but follows a curve rather than step downs. Notice the higher SOC at lower kW charging speeds before the step downs occur.
When charged > 90%, regen will be limited for the first part of your journey.
Lots of articles advise not charging to 100%, that may or may not be as true for EVs as for laptops and other devices that lack thermal conditioning, but why risk it? If 80% is adequate for daily needs, use it. When planning a longer trip, charge to 100%, and if possible target finishing the charge as close to departure time as possible to avoid sitting at 100% for lengthy periods.
There may be headroom at the top, above 100%. But it is not accessible, and some who have dug in deep claim Bolt has very little room past 100%. It isn't like volume measurements, it is a voltage question. Pack voltages are kept within "safe" ranges so as to not stress cells.
The 80% suggestion for public charging is as much about slow DCFC past 80% as it is opening access for others. On trips, your strategy plays out better by making more stops and keeping SOC in the faster part of the charging curve. Charging from 80-100% on DCFC probably takes more time than 20-60% in most cases, so you will make better time avoiding >80% in most cases.
Charging to 80% is not just about the charging time required but also for your battery's health. If you don't need the full range, keeping your battery in the 25-75% range is best for your lithium battery's life. That's why I charge to 80% except for long trips. Lithium-Ion Battery Care Guide - Part Four - CleanTechnica
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I'm with those who charge to less than full at home. I do believe charging to 80% is less stressful on the battery. My daily travels come nowhere near to needing using that 80%. The other advantage I find is that I don't have to go through that initial period of no one pedal driving that occurs when starting out with a 100% charged battery.
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I charge to 100% at home on 240v, but at lower rate to finish charging and balancing cells about an hour before I am going to use the Bolt. If I am NOT going to use the Bolt, I only charge to 80%. And I never charge over 80% on dcfc. I usually only charge to 90% on a commercial level 2, I don't want to spend more than 3 hours or so on a commercial level 2. I don't charge every day, usually do when the battery gets below 50%, never let it get below 25%, if possible.
How does a slower charge rate compare with delayed charging? i understand that the slower charge rate is healthier for a lithium battery, but if you are charging to 100 at a slower rate, does that mean your battery spends more time above 90% charge than with delayed charging (to 100)?
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I asked this question on the Wheel Bearings podcast (worth a listen if you like cars!), and the answer is - it doesn't matter. 12 kw is 12 kw, whether it takes ten minutes or ten hours to add those kw to your battery. There might be some marginal efficiency loss over the extended charging period, but we're talking pennies over the course of a monthly bill.
Great write up Rob. There’s a free 50kw DCFC on my way to work and there was no one there so figured I give the fast charging a try. I was surprised that it was only charging at around 34kw. My battery was a little more than 60% when I started so this makes sense now.
Thanks!
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50kW chargers are often 125A and are rated based on 400V. But 400V battery packs (in most EVs) don't reach 400V until near 100%.
For instance, a 400V/125A charger might be 50kW (400*125), but the Bolt at 50% is probably around 357-360V (referred to as nominal pack voltage) so it would charge at 44-45kW at its peak during the constant current (first) half of charging. Once you get into the constant voltage stage, current starts dropping and you start to see slower speeds.
Again, things changed with the 65kWh packs in 2020+ models, and this is what goes into older Bolts with replacement packs. So the curves rather than steps, and possibly sooner when it starts dropping amps. But the general idea should be similar to the graph.
It is helpful to understand the curve when doing long trips. charging to 50% or 60% is the fastest part of the curve, and if that gets you enough range to reach the next DCFC site, better to unplug then rather than go to higher charge levels. In roughly the same time you can go from 70-85%, you could go 20-60% at the next stop. It is never that cut and dry as gaps can be longer between sites, or less than ideal conditions (temp, terrain, etc) can make reaching a site difficult without going to higher state of charge.
On my 7100 mile trip, I averaged about 45 minutes per stop, but it was Feb-Apr and a bit cold in many places and I typically had to charge to 70-80% on many stops. On a summer trip to central AZ, I averaged about 30 minutes per stop, and was able to unplug around 60-70% at most stops. The warmer weather helped with efficiency so I didn't need to charge to as high of an SOC on the AZ trip as in the colder trip.
I think GM takes care of that for us, I don't think Bolt ever charges fast enough to cause damage. Watch News Coulomb videos on You Tube, Eric reached about 150K miles in less than 5 years on his 2017 Bolt, using DCFC nearly every week on 500 mile trips. He also charged to 100% for the first two years he owned his Bolt. He estimated less than 10% degradation at 150K miles.
So, while your comment surely holds true for Leaf, and maybe for other faster charging EVs, it may not be a big factor for Bolts.
I figure the general opinion on this forum knows best and my software limits me to 80% anyway. That being said, I've owned a couple of PHEVs, one of them is a 2018 and there is no control over charging %. You can either charge or not charge and it simply goes from 0 to 100. I've not observed any change in the useable all electric range of the Pacifica since 2018. My Fusion PHEV actually showed an improved all electric range going into year 3 before it was written off.
I know these batteries are smaller than the Bolt and that could have more to do with things but so far it hasn't affected them in any noticeable way.
It's also the way my wife likes it...just drive and plug it in when you get home or don't plug it in and just drive or whatever.
I know these batteries are smaller than the Bolt and that could have more to do with things but so far it hasn't affected them in any noticeable way.
It's also the way my wife likes it...just drive and plug it in when you get home or don't plug it in and just drive or whatever.
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OK, then is there a post about owners who have been monitoring battery to 100K miles? To me a wide range of owners reporting would make me believe in the battery. Sadly from every other use I still think 80% limit daily will prolong life of battery by a lot.
My answer to the original question is: yes. 
Charge to the level you need for your driving. In general, Li batteries should not be 100% charged all the time, so if you can manage your regular driving on 80% without routinely dropping below 20%, by all means do that; the battery will deteriorate more slowly. Charging to 100% at home can usually be done overnight on a Level 2 charger as easily as to 80%, and the Level 2 charge rate (see the charge curves posted above) doesn't really drop off until the battery state of charge is over about 90%, but in general charging to 100% should be done only when it's really needed for a trip or other reasons.
I did charge to 100% recently, for the first time in months, to make sure I would have enough charge to sit in a heated car during an expected extended power outage due to weather; so of course, being prepared, the outage didn't happen. No problem, I don't do it often, and the excess will burn off quickly with a few shopping or post office runs in cold, rainy weather. After which I'll turn hilltop mode on again - what the oldest Bolts (mine's a 2017) have instead of desired charge level, limits charge to about 90%.
As another noted, the recommendation to stop at 80% with a DC charger (away from home) is because the charge rate drops off a cliff at that point, so it's not worth it to cram that last 20% into the battery at DC charging prices, and with That Guy with an Audi or F150 waiting for your plug. You won't go quite as far starting at 80% on a road trip, but you still should be able to go for 2 hours or so; I've planned for 2 hours driving, 1 hour charging (and whatever else is needed during the stop), and it usually works out about like that.
Another reason for not charging to 100% if you don't really need it is regenerative braking. That's why they call the mode "hilltop" in the old Bolts. If the battery's 100% full, there's no room for adding charge while braking or going downhill. Starting at 80-90% gives you space for that even if you live up a hill (as I do).
Just some things to think about.
Charge to the level you need for your driving. In general, Li batteries should not be 100% charged all the time, so if you can manage your regular driving on 80% without routinely dropping below 20%, by all means do that; the battery will deteriorate more slowly. Charging to 100% at home can usually be done overnight on a Level 2 charger as easily as to 80%, and the Level 2 charge rate (see the charge curves posted above) doesn't really drop off until the battery state of charge is over about 90%, but in general charging to 100% should be done only when it's really needed for a trip or other reasons.
I did charge to 100% recently, for the first time in months, to make sure I would have enough charge to sit in a heated car during an expected extended power outage due to weather; so of course, being prepared, the outage didn't happen. No problem, I don't do it often, and the excess will burn off quickly with a few shopping or post office runs in cold, rainy weather. After which I'll turn hilltop mode on again - what the oldest Bolts (mine's a 2017) have instead of desired charge level, limits charge to about 90%.
As another noted, the recommendation to stop at 80% with a DC charger (away from home) is because the charge rate drops off a cliff at that point, so it's not worth it to cram that last 20% into the battery at DC charging prices, and with That Guy with an Audi or F150 waiting for your plug. You won't go quite as far starting at 80% on a road trip, but you still should be able to go for 2 hours or so; I've planned for 2 hours driving, 1 hour charging (and whatever else is needed during the stop), and it usually works out about like that.
Another reason for not charging to 100% if you don't really need it is regenerative braking. That's why they call the mode "hilltop" in the old Bolts. If the battery's 100% full, there's no room for adding charge while braking or going downhill. Starting at 80-90% gives you space for that even if you live up a hill (as I do).
Just some things to think about.
I’m the guy who asked the original question. Thanks to everyone who took the time to share their thoughts. I’m impressed with all the technical knowledge out there. It’s a lot to fathom, but I think I’ll continue to charge at 80% because it fits fine with my driving habits and necessary range on a day-to-day basis.
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Folks are quite correct that lithium ion batteries do not like being fully charged to 100% nor discharged to 0%. That will shorten their life. That's why your cell phone battery capacity goes to crap after 2 years. (And why I don't let mine sit on the charger overnight)
However, GM engineers are smart folks and thought of this. On the Volt (I've owned 3, and am waiting on a Bolt order), only the middle 80-something percent of the battery capacity is actually utilized. So at 'full' charge, the underlying battery is only at around 90%. Same at the bottom. Without doing this, there's no way an EV battery would maintain reasonable capacity past 2-3 years. I have to believe that the Bolt behaves the same way.
So in my opinion, don't sweat it, the GM engineers made it idiot proof for folks who aren't as thoughtful as all of us.
That said, as long as the vehicle doesn't need to be plugged in to keep the battery warm, 'manually' limiting charging to 90% may also give you a little longer battery life, as I'm sure GM was dancing on the line of 'what is best for the battery' vs 'how much range can we extract'.
Cheers
However, GM engineers are smart folks and thought of this. On the Volt (I've owned 3, and am waiting on a Bolt order), only the middle 80-something percent of the battery capacity is actually utilized. So at 'full' charge, the underlying battery is only at around 90%. Same at the bottom. Without doing this, there's no way an EV battery would maintain reasonable capacity past 2-3 years. I have to believe that the Bolt behaves the same way.
So in my opinion, don't sweat it, the GM engineers made it idiot proof for folks who aren't as thoughtful as all of us.
That said, as long as the vehicle doesn't need to be plugged in to keep the battery warm, 'manually' limiting charging to 90% may also give you a little longer battery life, as I'm sure GM was dancing on the line of 'what is best for the battery' vs 'how much range can we extract'.
Cheers
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