Charging - daily or not?

[HondaRacer]

This is a theoretical question about what’s best for the chemistry of the lithium battery packs. Let’s just say that most people should plug in when they need to and not worry about the little things.

That said, in theory which charging routine is better for the battery? Assume a driver uses 10-20% of charge in typical daily driving. Would it be healthier to recharge and replenish that use every night? Or to wait several days before charging? Do multiple small charge cycles have an effect on battery life?

We know that the battery is happiest near 50% SOC. Let’s discount that for this discussion. This is mostly about the effect of multiple charging cycles. Thanks.

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[ctenidae]

Interesting question.

One could postulate that the expansions and contractions that occur during charging and discharging are a big source of wear on the batteries (especially cathodes, iirc), so mechanically one could expect an improvement in battery life by reducing the number of such events. Since you can't really reduce the discharge events, you have to reduce the number of times you charge. You can't reduce your cycles by half, but you could get pretty close, I'd think - maybe take out 4 of every 10 (go from 5 discharge and 5 charge to 5 discharge and 1 charge).

Staying in the 20% to 80% seems to be the conventional wisdom from improved life, which would strongly imply a drive-it-until-it's-low strategy with a longer single charge back to 80%.

Tesla has more of a leave-it-plugged-in-all-the-time philosophy, I think. Musk was asked once something about some feature that somehow depended on the car being plugged in. He was confused, and wondered why anyone would ever not have their car plugged in at home. But, different battery design - maybe the cathodes (or anodes, I can't remember) are better at handling short frequent charge cycles rather than longer, deeper cycle charges.

 

[HondaRacer]

Interesting question.

One could postulate that the expansions and contractions that occur during charging and discharging are a big source of wear on the batteries (especially cathodes, iirc), so mechanically one could expect an improvement in battery life by reducing the number of such events. Since you can't really reduce the discharge events, you have to reduce the number of times you charge. You can't reduce your cycles by half, but you could get pretty close, I'd think - maybe take out 4 of every 10 (go from 5 discharge and 5 charge to 5 discharge and 1 charge).

Staying in the 20% to 80% seems to be the conventional wisdom from improved life, which would strongly imply a drive-it-until-it's-low strategy with a longer single charge back to 80%.

Tesla has more of a leave-it-plugged-in-all-the-time philosophy, I think. Musk was asked once something about some feature that somehow depended on the car being plugged in. He was confused, and wondered why anyone would ever not have their car plugged in at home. But, different battery design - maybe the cathodes (or anodes, I can't remember) are better at handling short frequent charge cycles rather than longer, deeper cycle charges.

I could see Tesla or any OEM saying just plug it in and leave it to promote ease of use. Most people don’t want to fret over optimum battery care. But I would agree that it seems to make sense to reduce the number of charge cycles, although the net result may be rather insignificant.

 

[Vulnox]

I would think more frequent and shorter charges would be best as long as you are only charging up to 85-90%. The longer you are charging the longer the components are heat soaking. A part in a higher heat situation for an hour is less likely to suffer fatigue issues than one in a high heat situation for three hours.

That said, it's an 8 year/100k mile warranty on the battery, I think I would just do what fit best into my usage of the vehicle.

 

[generaltso]

I think worrying about this is a barrier to EV adoption. Just charge when you want and drive when you want.

 

[HondaRacer]

I think worrying about this is a barrier to EV adoption. Just charge when you want and drive when you want.

I agree. It’s not a worry, just a theoretical question. Some people like to get more into the weeds on these things.

 

[ctenidae]

I think worrying about this is a barrier to EV adoption. Just charge when you want and drive when you want.

Totally agree, and that's kind of why these conversations have to happen. "Charge as it works for you" is the right answer, but it's not widely enough known or accepted as conventional wisdom yet. It's totally a barrier, all wrapped up under the umbrella of "range anxiety"- that general uncertainty about things that makes it harder to act.

When, where, and how to get gasoline used to be a big barrier to buying a car. Same thing now for electrons. However, this transition will probably make the next one (hydrogen? Mr. Fusion?) easier.

 

[DYohn]

I agree. It’s not a worry, just a theoretical question. Some people like to get more into the weeds on these things.

I let the battery design engineers worry about those weeds. I'm a user, not a battery designer.

 

[Ghost Ryder]

isn't there already a 9kw reserve, so when you charge to 100%, is that really 100% or 91% of the total battery pack?

 

[harrypags]

I spoke with an engineer who worked for Daimler a couple months ago while charging my MME. They were testing the 350Kwh fast charger on their new electric Freightliner. Pretty cool to see a huge truck charging!

Anyway, He had experience with EVs and owned a few in the past including an electric Focus and Model 3. He said EV batteries will last longer and perform better if you allow them to deplete to 10% before charging. When it is time to charge, you should only "fill up" to 80%. Basically, he recommended charging to 80% and not charging again until you're at 10%.

Personally, I try to follow this guideline but if I have places to go and need the range, I'll just charge up to 100%. I won't have the car at the end of it's battery life so it's longevity doesn't really matter to me at the end of the day.

 

[ADDZ71]

I don't know if I would follow the advice of the Freightliner engineer. Charge cycles are charge cycles (60% is = 2 X 30%). Your battery has finite amount of charge cycles that are more impacted by the depth of discharge and length of time at full capacity. Ford has reduced this impact by not allowing usage at the ends of the curve. I believe in the ABC philosophy of "always be charging". That provides support to the ancillary equipment to keep temps happy.

 

[RickMachE]

Three of the many, many threads.

https://www.macheforum.com/site/threads/80-charge-or-90-charge-for-daily-use.21158/
https://www.macheforum.com/site/thr...ging-at-home-what-threshold-do-you-use.18229/
https://www.macheforum.com/site/threads/best-charging-for-battery-life🔋-mach-e-gt.20559/#post-485272

 

[Blue highway]

I agree. It’s not a worry, just a theoretical question. Some people like to get more into the weeds on these things.

Two things are true at the same time.

1 - lots of short charging cycles keeping the battery close to 50% is much better for the battery than deep cycling. There are lots of research papers on this.

2 - In a practical sense, charge to less than 100% daily, and enjoy the car. The cooling system and software pad to keep you from true 100% or 0% saves most users from themselves.

 

[generaltso]

isn't there already a 9kw reserve

kWh

They were testing the 350Kwh fast charger

kW

Sorry, I don't usually go out of my way to correct this since kW and kWh are used incorrectly so much of the time, but seeing two in a row that used the opposite and BOTH ended up being wrong just pushed me over the edge.

Carry on.

 

[Mach-Lee]

This is a theoretical question about what’s best for the chemistry of the lithium battery packs. Let’s just say that most people should plug in when they need to and not worry about the little things.

That said, in theory which charging routine is better for the battery? Assume a driver uses 10-20% of charge in typical daily driving. Would it be healthier to recharge and replenish that use every night? Or to wait several days before charging? Do multiple small charge cycles have an effect on battery life?

We know that the battery is happiest near 50% SOC. Let’s discount that for this discussion. This is mostly about the effect of multiple charging cycles. Thanks.

I say let it run down some before recharging. For a couple reasons:

• Time at high SoC is worse for the pack. If you go 80-90% everyday the average SoC is 85%, vs. if you go down to 30%-90% it would be 60%.
• Repeated shallow charge/discharge cycles increase the error of the SoC display (coulomb counter), especially when they are in the middle of the range with little voltage variation. The next time the pack is drawn down to a low SoC the range estimate could be drastically off.
• It is more efficient to heat or cool the pack in one large charging session than many small ones. Especially in cold weather, it will take 1-2 kWh to heat the pack each time the car is charged.
• Not plugging in all the time is less wear and tear on the charge port.

I like the idea of charging a minimum of 10% each time to reduce unnecessary charge cycles. At home I don't plug in until I'm below 50% and charge to about 80%. I think that provides a good balance of available range and minimizing battery stress from sitting at high voltage.

However all this is trumped by a message about plugging in for thermal management. If it's really hot or cold outside you should always plug in when told so the pack can be brought to an acceptable temp range. If you live in Phoenix, you need to plug in whenever you can so the battery can be cooled. Extreme climates may be the origin of the recommendation to frequently charge, it is not necessary at moderate temps.

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