Extending battery life

[Tarrngtn]

I think there is already a thread on this, but I would like an update from people who really know about electrical engineering and can comment from some expertise. I have read that battery life is extended if we: 1) use hilltop reserve so the batter is not fully charged up; and 2) recharge only after the battery is significantly discharged. Does #2 mean down by half, down by two-thirds, down by three-quarters?? Thanks for the expertise of other owners.

 

[RickCH]

The expertise on this topic is based on chemistry, not EE, and this is the expert that Tesla contracts: https://www.dal.ca/diff/dahn/about.html

Jeff Dahn's simple recommendation is to charge up to 70%, and to 100% when needed. He hasn't said anything specifically about the low end, but that's probably because the car's management system won't let the charge to drop to the danger levels.

If you really want to go down the rabbit hole, here's his lecture, "Why do Li-ion batteries die and can they be immortal?". https://youtu.be/9qi03QawZEk

 

[WetEV]

{Does recharge only after the battery is significantly discharged} mean down by half, down by two-thirds, down by three-quarters??

With hilltop reserve on, this probably doesn't matter very much. If hilltop reserve was at 70% rather than about 90%, it wouldn't matter at all.

Charging to 100%, then discharging and recharging by a tiny amount will degrade a battery more quickly than charging to lower percentage and doing the same discharge and recharging cycles.

 

[SparkE]

My approach has been :
- do not fully charge unless it is needed (which isn't often in a Bolt, unless you have a 200+ mile commute) ; I would charge to about 80% (either manually stopping the charge, OR setting the timer to start charge so that it would be about 70% when I got up). It wasn't that difficult for me, as I rarely drive more than 30 miles a day, so plugging in for 90 minutes or 2 hours got me back to 70-80%.
- when you do charge to 100%, don't let the car sit for a long time at full charge. I would set the charge timer so that it would reach 100% about an hour or 90 minutes before my departure.
- do not charge when the battery is hot - heat kills Li-Ion batteries. Repeated hot charges (and discharges) are bad, bad, bad. I used to even wait an hour or two before plugging the car in to charge after I got home, and wait to charge late at night after the temp had dropped on really hot days - OR, plug in the 120V OEM EVSE on really hot days, so that the car would run it's battery temp mgmt system to keep the battery cooler while still not putting in juice at a fast rate - then plug the car into 240V late at night, or even skip it for a day.
- do not park in full sun for long periods (like when at work) on HOT days (over 85 or 90). The battery will get heated up over the hours that you are at work. I have a friend who talked his employer into letting him install one of those canvas-and-aluminum portable car-ports at the back of the parking lot (with a reserved for <license plate> sign) so that his EV was always in the shade. He'd put it up around June and take it down in early October.
- rarely DCFC (only when needed). DCFC heats up the battery cells. The faster you charge, the more heat accumulates in the battery, especially as you reach 80% or higher. (It also depends on how much you put in - charging from 10% to 80% will generate a lot more heat than charging from 55% to 80%.)
- let the car charge to 100% about once every 4-6 weeks to let the battery do cell balancing, if needed.

So I wasn't a maniac about it - if I needed it, I did it. If I forgot and occasionally charged to 100%, no biggie. I was just trying to set my *default* mode to protect the battery as much as possible. I figured that if I did a full charge (maybe) 2 or 3 times a month, instead of every night, that I was prolonging the life of my battery. And they are easy habits to get into - I actually bought a super-cheap kitchen timer that I always had set to 60 minutes and I stuck in to my fridge door, which I would turn on when I got home (unless I forgot - then I'd see it when I got food out of the fridge, and remember to charge anyways). When it went off, I'd hook the car up to charge.

Now some of these are "extreme" - but only in the sense that they might not be needed, so they are a 'waste of time'. But my outlook was that they are really easy to make 'the default', they don't take up much time, and just the *chance* that these actions might increase the battery life (and range) was enough for me to add an extra 30 seconds a day into my routine. Again, I didn't obsess about them, I just tried to do them most of the time.

 

[SparkEVPilot]

My approach has been :
- do not fully charge unless it is needed (which isn't often in a Bolt, unless you have a 200+ mile commute) ; I would charge to about 80% (either manually stopping the charge, OR setting the timer to start charge so that it would be about 70% when I got up). It wasn't that difficult for me, as I rarely drive more than 30 miles a day, so plugging in for 90 minutes or 2 hours got me back to 70-80%.
- when you do charge to 100%, don't let the car sit for a long time at full charge. I would set the charge timer so that it would reach 100% about an hour or 90 minutes before my departure.
- do not charge when the battery is hot - heat kills Li-Ion batteries. Repeated hot charges (and discharges) are bad, bad, bad. I used to even wait an hour or two before plugging the car in to charge after I got home, and wait to charge late at night after the temp had dropped on really hot days - OR, plug in the 120V OEM EVSE on really hot days, so that the car would run it's battery temp mgmt system to keep the battery cooler while still not putting in juice at a fast rate - then plug the car into 240V late at night, or even skip it for a day.
- do not park in full sun for long periods (like when at work) on HOT days (over 85 or 90). The battery will get heated up over the hours that you are at work. I have a friend who talked his employer into letting him install one of those canvas-and-aluminum portable car-ports at the back of the parking lot (with a reserved for <license plate> sign) so that his EV was always in the shade. He'd put it up around June and take it down in early October.
- rarely DCFC (only when needed). DCFC heats up the battery cells. The faster you charge, the more heat accumulates in the battery, especially as you reach 80% or higher. (It also depends on how much you put in - charging from 10% to 80% will generate a lot more heat than charging from 55% to 80%.)
- let the car charge to 100% about once every 4-6 weeks to let the battery do cell balancing, if needed.

So I wasn't a maniac about it - if I needed it, I did it. If I forgot and occasionally charged to 100%, no biggie. I was just trying to set my *default* mode to protect the battery as much as possible. I figured that if I did a full charge (maybe) 2 or 3 times a month, instead of every night, that I was prolonging the life of my battery. And they are easy habits to get into - I actually bought a super-cheap kitchen timer that I always had set to 60 minutes and I stuck in to my fridge door, which I would turn on when I got home (unless I forgot - then I'd see it when I got food out of the fridge, and remember to charge anyways). When it went off, I'd hook the car up to charge.

Now some of these are "extreme" - but only in the sense that they might not be needed, so they are a 'waste of time'. But my outlook was that they are really easy to make 'the default', they don't take up much time, and just the *chance* that these actions might increase the battery life (and range) was enough for me to add an extra 30 seconds a day into my routine. Again, I didn't obsess about them, I just tried to do them most of the time.

WISE WORDS OF WISDOM WORTH FOLLOWING!!

 

[Tarrngtn]

OK. So we should continue without recharging until it is perhaps down to 25% or less, then recharge to 75% or so. The only exception would be if we are planning a long trip for the next day. Also, try to keep the garage as cool as possible but above freezing. Doable. Thanks for the info. The lecture on battery chemistry was very informative.

 

[BillHowland]

OK. So we should continue without recharging until it is perhaps down to 25% or less, then recharge to 75% or so. The only exception would be if we are planning a long trip for the next day. Also, try to keep the garage as cool as possible but above freezing. Doable. Thanks for the info. The lecture on battery chemistry was very informative.

I've driven my 2017 27,000 miles and haven't noticed any decrease in range as of yet, and I often charge to 100%.

That is what is great about GM products... You get a pretty good battery with them. I'd be interested in hearing from ANYONE who has noticed any loss so far under any circumstances.

 

[GetOffYourGas]

OK. So we should continue without recharging until it is perhaps down to 25% or less, then recharge to 75% or so. The only exception would be if we are planning a long trip for the next day. Also, try to keep the garage as cool as possible but above freezing. Doable. Thanks for the info. The lecture on battery chemistry was very informative.

I've driven my 2017 27,000 miles and haven't noticed any decrease in range as of yet, and I often charge to 100%.

That is what is great about GM products... You get a pretty good battery with them. I'd be interested in hearing from ANYONE who has noticed any loss so far under any circumstances.

I know you don't have the DCFC option, Bill, but those that do can still only charge at up to 55kW. The Tesla fans love to brag that they charge up to 120kW. Given GM's conservative approach to things versus Tesla's very liberal, I wonder if that 2.2x faster charging causes extra stress and degradation, or if it really is just a difference of chemistry.

 

[mwk]

So I have a 5 mile commute each way to work. Typically, I'll plug my car in once a week or so, but leave it overnight so it's full the next day. I haven't really had the car discharged under 50% except for one longer road trip where it got down to around 30%.

However, 99% of my charging has been done via the 120v EVSE that came with my car. I plug it in at home, most of the time.

So, does using that 120v charger help to preserve the battery life?

 

[Tarrngtn]

If my intent is to wait until I am down to about 20% charge and then recharge to about 80%, can it be done remotely? My plan is to set off-peak from midnight to 4AM, and set leave time at 4AM as well. Peak time is set for 4AM to midnight. And it is set for off-peak charging. If the car is down to 20% and I plug it in at say 11:30 or so, will it begin to charge at midnight and stop at 4AM? Or will the programming preference to leave me fully charged override my off-peak charging and leave time instructions? Or would I be doing it incorrectly? The owners manual is not clear on this point, or at least I can’t find where the clarity is found. I have a level 2 charger in the garage.

 

[SparkE]

<span>If my intent is to wait until I am down to about 20% charge and then recharge to about 80%, can it be done remotely? My plan is to set off-peak from midnight to 4AM, and set leave time at 4AM as well. Peak time is set for 4AM to midnight. And it is set for off-peak charging. If the car is down to 20% and I plug it in at say 11:30 or so, will it begin to charge at midnight and stop at 4AM? Or will the programming preference to leave me fully charged override my off-peak charging and leave time instructions? Or would I be doing it incorrectly? The owners manual is not clear on this point, or at least I can’t find where the clarity is found. I have a level 2 <a href="http://www.amazon.com/s/?field-keywords=electric%20vehicle%20charger&tag=myelecarfor-20" class="interlinkr" target="_blank">charger</a> in the garage.</span>

I believe that it depends on which combination of charging parameters you have set.

Delayed charge? Departure Charge? Off-peak only charge? Priority Charge? (pg. 129) . Location-based Charge?

For one thing, If "Priority Charge" is set, then the battery will immediately start charging until the battery is at 40%, then stop until the other conditions are met before resuming charging.

On Pg 125
Charge Mode Selection

Departure :
The vehicle will schedule charging to complete by the programmed departure time. The vehicle estimates the charging schedule based on programmed departure times, charge rate limits, electric rate preference and schedule, and priority charging settings.

Also, on page 127 it says : "if the selected electric rate settings result in a very long charge completion time, the vehicle will start charging immediately upon plug-in."

So, it appears that using departure charge mode means that the car will start charging at just the right time to guarantee a full charge at your departure time (90% if you are using Hilltop Reserve) - ignoring the rate info If it can't charge the car fully charging only during off-peak.

It seems that your best bet is to figure out at what time your off-peak rate ends (which is when you want to stop charging, I assume). You figure out your charging rate (kW) and calculate how long it would take your car to charge to (say) 70-80%, then calculate your departure time to be just far enough past off-peak such that your battery would be at 70% full at the time that off-peak ends.

Example:

Your level-2 EVSE and 240V circuit & breaker can provide 32A. 32A * 240V = 7680W (7.6kW), but the vehicle only draw a max of 7.2 kW, correct?

Your off-peak ends at 7 a.m.

You want to end the charge at about 70% SoC. You have hilltop reserve set (only charges to ~88% SoC). You need to calculate how long it would take to charge from 70% to 88%.
- The battery is rated at 60 kWh. 18% of 60 is 10.8 kWh.
- at 7.2 kW, you will get 7.2 kWh per hour (duh). 10.8/7.2 is 1.5. So, you program your departure time to be 1.5 hours AFTER off-peak ends.

However, that means that you must go out and unplug the vehicle just before off-peak ends if you want to charge at off-peak rates, meaning that you would be getting up at 7 a.m. any morning that you wanted to do this.


OR :

Just set hilltop reserve, and set the departure time to be 30 mins before peak rate ends, and simply plug in the car. It will start charging at the proper time to have the battery 'full' (about 88% of the 'usable' capacity) just before peak rates end. Since the 'usable' capacity is about 90-92% of the actual 'full-rated' capacity (based on calculation of the battery capacity by multiplying # of cell/packets in the battery), filling to about 90% of 'usable' capacity is filling to about 80-82% of rated capacity. And if on work days you are up before 6:30 anyways, you can simply walk out to the garage and unplug before it gets to 88% full.

And personally, I wouldn't ever let the charge go below 35-40% SoC during everyday (non-travel) use. Not because of battery longevity, but because I would always want to be able to jump in the car and drive a minimum 80 miles without having to think about it.

 

[oilerlord]

"Just set hilltop reserve, and set the departure time to be 30 mins before peak rate ends, and simply plug in the car. It will start charging at the proper time to have the battery 'full' (about 88% of the 'usable' capacity) just before peak rates end. Since the 'usable' capacity is about 90-92% of the actual 'full-rated' capacity (based on calculation of the battery capacity by multiplying # of cell/packets in the battery), filling to about 90% of 'usable' capacity is filling to about 80-82% of rated capacity."

Hey Mr. Spark!

I've been away from this forum for a while. Sound advice on extending battery life. So, to be clear...what percentage of total battery capacity is used when hilltop mode is engaged? The last time I was here, there was a debate on how deep GM allows you to go into total battery capacity.

My B250e is limited to use only 28 kWh (about 78%) of it's 36 kWh total battery capacity. From my experience with the car, after almost 50,000KM (31,000 miles), the summer range hasn't skipped a beat. I turned a personal best of 201 km (124 miles) just a few weeks ago. Not bad for a 4 year old car with some miles on it. I have no doubt this is due to Mercedes / Tesla sacrificing range for battery longevity. With that said, winter is still a grind. A used Bolt is definitely in our future.

To SparkE's point, I think anyone that intends to own a Bolt for the long term NEEDS to use hilltop mode on a regular basis. Be kind to the battery, and it will be kind to you.

 

[Tarrngtn]

Thank you Sparke and Oilerlord for taking the time to deal with me. I did all that stuff last night and here is what happened. When I plugged in at 11:30 it began to charge right away, not waiting for midnight which I have set as off-peak. That is OK since I don’t have time-of-day pricing. I am just trying to be a good citizen by charging when the load on the grid is at minimum. So 11:30 or so is OK. Next morning I had 90% charged — ie down two bars. That is OK with me for the top charge. But I wonder: If I had it set to charge on demand and hilltop reserve set would’t I get the same results by plugging it in at 11:30? It would charge immediately and end at 4:00 or so down two bars because of hilltop reserve. Yes?

 

[SparkE]

Thank you Sparke and Oilerlord for taking the time to deal with me. I did all that stuff last night and here is what happened. When I plugged in at 11:30 it began to charge right away, not waiting for midnight which I have set as off-peak. That is OK since I don’t have time-of-day pricing. I am just trying to be a good citizen by charging when the load on the grid is at minimum. So 11:30 or so is OK. Next morning I had 90% charged — ie down two bars. That is OK with me for the top charge. But I wonder: If I had it set to charge on demand and hilltop reserve set would’t I get the same results by plugging it in at 11:30? It would charge immediately and end at 4:00 or so down two bars because of hilltop reserve. Yes?

I think so. I would definitely set hilltop reserve, EXCEPT those times when you expect to drive over 180-200 miles the next day. (Well, if you were planning on driving 290 miles round-trip, 145 miles each way, it wouldn't really matter if a DCFC was in a convenient location.) You can tell the car to ignore all charging settings by using 'temporary override' (page 129-130) or, even easier, "Delayed Charging Override" (page 235), which is (1) plug in J1772 plug to charge port and wait 5-10 seconds, (2) unplug J1772 plug, then (3) WITHIN 5 SECONDS, plug the J1772 connector back into the car. You will hear a single 'chirp' and the light on the dash should show that the car is charging. You can also set the car to only do delayed charging at home (i.e., location based parameters such that when you plug the car in away from home, you get 'immediate charge').

But, back to your question, I would set the 'peak' hours to end later than 4 a.m. (6 a.m.? 7 a.m.?) so that when you DO have a deep discharge and need a lot of electrons, there will be enough time to fully charge the vehicle during 'low usage' times. (10% up to 90% will take close to 7 hours on a 32A/240V EVSE. If you simply make a "converter pigtail" to be able to plug the stock EVSE into 240V, making it a 12A/240V {2.88 kW} EVSE, every 10% of charge will take about 2 hours. I have a 16A/240V EVSE from a previous vehicle {3.8 kW} and a 10-hour charge would add approx 38 kWh into the battery, about 65% of a full charge, maybe 160 miles. )

 

[iletric]

This 80% charging or charging 100% as close as to departure to save battery has been debunked since Leaf 1.

The best way to protect the the battery, having gone through Leaf 1, Spark EV, Kia Soul EV and owning 2 Bolts since 2017, is to limit deep discharges. This is why Bolt is holding up so well--I have never discharged any of them to 1 blink. There is no issue charging it up to 100% every night.

My 2017 Bolt's range has not dropped a bit after 35,000 miles, in fact, it even seems like its range has increased over time. I routinely see 260 mile range (in summer).

 

[BoltEV]

I have to agree: my 2017 Bolt EV has 21,500 miles and shows NO noticable loss of battery capacity even though I faithfully charge my Bolt up to 100% every night.

There was a flurry of posts on this forum one year ago from non-Bolt EV drivers (mostly Leaf and a Mercedes driver) who spoke from experience that is totally not relevant to how GM has engineered the Bolt battery and scared most people into not taking advantage of the capacity of their batteries.

Sort of a "drive it less now, so that you can drive it more later" philosophy that is obviously not holding up in time.from anecdotal experiences.

 

[plj]

I posted discussion of an academic paper on extending Li-ion battery life here: https://www.mychevybolt.com/forum/viewtopic.php?f=12&t=8080&p=31226#p31226

They suggest charging "as late as possible." That is, not not routinely charging it. They say that charging as late as possible can double battery life.

 

[BoltEV]

So, does using that 120v charger help to preserve the battery life?

No

Some do a DIY adapter so that the 120v charger will plug into and accept 240v and work at 12 amps for faster charging.

 

[mrp10000]

This 80% charging or charging 100% as close as to departure to save battery has been debunked since Leaf 1.

The best way to protect the the battery, having gone through Leaf 1, Spark EV, Kia Soul EV and owning 2 Bolts since 2017, is to limit deep discharges. This is why Bolt is holding up so well--I have never discharged any of them to 1 blink. There is no issue charging it up to 100% every night.

My 2017 Bolt's range has not dropped a bit after 35,000 miles, in fact, it even seems like its range has increased over time. I routinely see 260 mile range (in summer).

I drove a LEAF for a year and a half, and almost overnight last fall, lost about 5% of the battery. It must have been the summer weather here in NC...Anyway, I inherited the wife's Bolt (after waiting two years her Model 3 arrived!) which is 14 months old and has 13,500 miles. We generally keep it between 25% and hilltop reserve. I drove 1,300 miles this week, including 3 fast charges. Seems to be holding up. Leaving home this morning, midrange showed 289 miles (with air conditioning turned off and 263 beginning midrange when on). We charge to full for a trips involving 100 miles or more and keep it at hilltop reserve the rest of the time. We just charge when we get worried we may need the extra mileage, and we definitely do not do any deep discharges.

 

[Anonymous]

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