Long Term Battery Care and Charging Habits

[Dave EV]

I suspect the S does the same now, or by the time summer comes on, updates will provide fine tuning.

At the very least, at least the S doesn't bother to heat the pack unless it's actually charging or on. Definitely the most efficient way to do it.

The Roadster most definitely does balance with a Standard charge. However, it does something more after a Range charge. I've been told this by various Rangers, and have seen clear evidence myself that they are correct. Exactly what "more" is done is not clear.

Nor is it clear that the Model S works the same way.

It's very likely that the Model S works the same way. The BMS system probably looks for differences in cell/sheet or however else it's grouped the pack. The voltage characteristics of most lithium cells is such that there is very little voltage change in the middle of the SOC band, but the voltage difference increases when the SOC of a cell is either very low or very high.

This makes it easier to spot cells that are out of balance when the pack is either fully discharged or fully charged.

The BMS system most likely looks for a minimal amount of voltage difference before it starts to bleed off high voltage cell(s). When the pack is fully charged, it's easier to find cells with a big enough voltage difference to trigger balancing actions.

 

[SFOTurtle]

So, if I'm only putting about 20 miles on my car every day or so, I assume it is better to plug into 110 at night, charge for about 8 hours through the night, and then repeat the next night. It seems like I should avoid using the 240 unless I am low on charge and need to replenish before a long trip the next day.

 

[westom]

So, if I'm only putting about 20 miles on my car every day or so, I assume it is better to plug into 110 at night, charge for about 8 hours through the night, and then repeat the next night.

Many statements are confusing. Characteristic of lithium batteries and what Tesla does (its algorithm) are two different (although related) topics. How a battery reacts is different from what Tesla might do to avert problems.

Lithium batteries cannot be slow charged for some technology reasons. For example, a 'fully charged' state is unknown if the charge rate is too low. The battery must be charges at a high rate to maybe learn the battery was already fully charged.

Second, lithium batteries do not charge reliably at low rates.

Third, temperature is mostly irrelevant when using the battery. But temperature extremes can be harmful when recharging the battery.

These and other points were made in a previous post.

Now, what does Tesla do to work around or protect from lithium battery characteristics. Tesla algorithms are a separate discussion. Does Tesla's algorithm know a battery charge state without 'discovering by charging'? How deep does the Tesla permit battery discharge before declaring the battery depleted? Use of percentage is a vague number. Does 50% mean a battery 50% discharged OR 50% of what Tesla permits for discharging?

Experience with lead acid batteries says little useful. That technology is seriously different from nickel based and lithium based batteries. Manufacturer charge algorithms for this charger are more complex and significantly different. Again, discussion must separate battery behavior and care from Tesla's charger algorithms.

 

[100thMonkey]

I noticed today after the car sat out all night while our Leaf charged that the S's regen was limited, presumably to protect the cold soaked battery from being charged at a damaging level while cold. when I cam home today I plugged the car in then stopped the charge from the phone app, leaving it plugged in. curious to see if the battery stays warmer overnight since it's plugged in, even though it's not charged. at the very least, with it being plugged in, it makes it easy in the morning to top up and precondition both the battery and the cabin.

 

[smorgasbord]

Roadster owners have had this discussion ad nausum, and nothing Tesla has said indicates that Model S is any different in these regards:

1) Keep the car plugged in whenever you can. That means even if it's charged.
2) Charge in Standard mode whenever you charge, as long as you don't need the extra range.
3) Charge the car every chance you get. If your commute is 5 miles, don't wait until the weekend to charge - charge every night. More light cycles better than fewer deep cycles.
4) Don't worry about charging the battery too quickly. Your Tesla is built to handle it. On Roadster, consensus is that 30-40amps (UMC max) is just about the most efficient. Going faster heats up the battery more, so it diverts juice to cool it, and charging slower provides no benefits. But, do not worry about 70/80 amp charging. Heck, SuperCharging doesn't hurt the battery.
5) If you need a Range charge, best to do a Standard charge first, then start the Range charge so that it completes about 15 minutes before you start your drive. That way the batteries don't sit completely full for long. Although Tesla will use wall energy to keep the batteries cool to reduce damage, doing that a lot will lead to quicker degradation. Note that leaving the car fully charged in Range mode once in a while is OK, and provides a benefit of battery balancing. But, keep the car plugged in when it's full in Range mode!
6) After a hard drive in hot weather, your battery may be warm or even hot, so even though your Tesla will cool the battery if it's really hot, the Tesla algorithms are compromises between battery life and power consumption. If it's not plugged in, your Tesla doesn't know if it's OK to use juice to cool the battery since you might want that juice for driving. So, it doesn't cool the battery down as much as is optimal for longest life. Therefore, after a spirited drive, it's best to plug the car in and charge right away since that cools the battery to a lower temp than otherwise.
7) If you're on a TOU meter, you may not want to charge as soon as you get home, even if the battery's hot. Doing a Range charge at 240volts, 13 amps for 20 minutes or so will force the car to cool down the battery but not use too much juice. When the battery temp drops below 80 degrees F manually stop the charge and reset charge mode to Standard. I use OVMS to monitor the battery temp and setup the charge modes on my Roadster.
8) It's just fine to have the car sit at full Standard charge while plugged in for weeks at a time. Roadster has a "Storage Mode" (Model S doesn't), but I've never heard any Tesla employee advise anyone to actually use it. Maybe if you're not going to drive the car for months or something.
9) Avoid letting the car sit at low charge levels for long periods of time. This may be more of a problem with Roadster than Model S, but if you can avoid it you should avoid it.

 

[Hans (Amsterdam)]

@smorgasbord

3) Charge the car every chance you get. If your commute is 5 miles, don't wait until the weekend to charge - charge every night. More light cycles better than fewer deep cycles.

Can you refer to any data/research that would proof this ? I suppose that deep charges one or two times a week lead to a long term lower average SOC resulting in a longer battery life.

 

[jerry33]

I suppose that deep charges one or two times a week lead to a long term lower average SOC resulting in a longer battery life.

That is incorrect. Shallow cycling is far better for battery longevity. For example a battery may have a life of 300 full cycles, 1,200 half cycles, and 2,000 quarter cycles (example numbers only. link here).

 

[Dave EV]

That is incorrect. Shallow cycling is far better for battery longevity. For example a battery may have a life of 300 full cycles, 1,200 half cycles, and 2,000 quarter cycles (example numbers only. link here).

Whether or not shallow vs deep cycles is better for calendar life depends on a number of variables - two key ones are battery pack temperature and time spent at a specific SOC.

A lithium cell sitting at 80% SOC will undoubtedly lose capacity faster than one sitting at 50% SOC - the question is how much faster...

 

[djp]

On my Roadster I generally do shallow cycles between 30% and 50% SOC to keep a low average SOC. I only charge in Standard Mode when I need the distance, effectively treating Standard Mode like Range Model.

The battery pack has been staying in balance, but it's too early to say if its life has been extended. The Roadster battery studies being done on this forum will be interesting to watch but so far have limited data.

 

[cdabel]

I have an interresting commute. I live 200 meters over sealevel, and my office is down at the harbour. With my previous EV many years ago, I would end up at work with more energy than I started with because of regen. I' m guessing regen on the Model S is even better, so I'm not sure I really want to top off completely. It seems like a waste of perfectly good potential energy. Its a short commute, so would charging every other day or so be OK?

 

[smorgasbord]

Whether or not shallow vs deep cycles is better for calendar life depends on a number of variables - two key ones are battery pack temperature and time spent at a specific SOC.
A lithium cell sitting at 80% SOC will undoubtedly lose capacity faster than one sitting at 50% SOC - the question is how much faster...

The problem is that there are competing factors at play. Tesla only recommends Storage Mode on Roadster when you're not using the car for more than 2 weeks. Even at a 2 week trip, they told me to keep it at Standard.

- - - Updated - - -

On my Roadster I generally do shallow cycles between 30% and 50% SOC to keep a low average SOC. I only charge in Standard Mode when I need the distance, effectively treating Standard Mode like Range Model.

If you like to use full acceleration, you're probably putting more stress on your battery. Full acceleration at less than half charge isn't good for the battery, and I'll wager it's worse than charging all the way up in Standard Mode.

Again, there are competing factors. It's hard for us to know better than Tesla what's best for our batteries.

 

[westom]

It seems like a waste of perfectly good potential energy. Its a short commute, so would charging every other day or so be OK?

The battery will only take the energy it needs. However this (the nature of lithium batteries which is different from how Tesla might do it) was posted previously. A battery must take a full charge current at the beginning to 'learn' the battery's actual state. If a battery is already fully charged, then the battey is being overcharged at a full current until the charger can learn what state the battery is at.

That is the nature of charging a battery. How does Tesla do it or avoid that problem? That is a completely different answer. You must know both answers to have a useful reply (no speculation). Without both answers, I would avoid charging until a battery is surely at or below maybe 90%. To 'maybe' extend battery life expectancy.

 

[Dave EV]

Huh? Resting voltage of a lithium battery is a perfectly acceptable way of estimating SOC...

 

[westom]

Huh? Resting voltage of a lithium battery is a perfectly acceptable way of estimating SOC...

As the battery is topped off, its voltage drops (does not increase). Voltage only increases during most of a charge. But not at the end.

 

[djp]

TIf you like to use full acceleration, you're probably putting more stress on your battery. Full acceleration at less than half charge isn't good for the battery, and I'll wager it's worse than charging all the way up in Standard Mode.

Again, there are competing factors. It's hard for us to know better than Tesla what's best for our batteries.

After three years I have zero battery degradation, so the shallow charges seem to be working fairly well.

I generally run at 50% SOC during the week when I'm using the Roadster for commuting and not doing hard acceleration, and do Standard charges on weekends when I'm more likely to have fun with the car. The Tesla default is a trade-off between battery life and range that doesn't take into account how the car is actually going to be used. My theory is that I can do a better job at managing the SOC since I know ahead of time the type of driving I'll be doing and can charge to an appropriate level.

Agreed there are many competing factors. Rich and Tom's battery studies should help shed some light on the relative effects of mileage, calendar life, charge cycles, SOC, temperature and current draw.

 

[Dave EV]

As the battery is topped off, its voltage drops (does not increase). Voltage only increases during most of a charge. But not at the end.

I do believe you are mistaking the voltage characteristics of NiCd or NiMH batteries rather than Lithium batteries.

For lithium cells, the standard charging algorithm follows a constant current charge profile until the cutoff voltage is reached, then the charging algorithm switches to a constant voltage profile where current is slowly reduced while maintaining the desired cutoff voltage. Once current drops below some point the charge is determined to be finished. During the constant current phase battery voltage will steadily rise. At no point does the voltage drop.

For NiCd/NiMH cells, the cell voltage drops slightly after 100% SOC is reached. Note that if these cells were used in an automotive application, it's highly unlikely that you'd be charging to 100% SOC even though NiCd/NiMH can tolerate this to some degree. Charging a Lithium cell too 100% is generally very risky (lithium cells do not like overcharging at all in general) and drastically shortens it's life. For this reason, no commercial application which requires durability will charge more than mid-high 90% SOC at most.

 

[Hans (Amsterdam)]

 

[Robert.Boston]

As those charts show, @Hans, there is a non-linear relationship between SOC and the effect of time. I'd be reluctant to draw inferences about the impact of storing at 50% vs. 90% from this data.

 

[stevezzzz]

I have an interresting commute. I live 200 meters over sealevel, and my office is down at the harbour. With my previous EV many years ago, I would end up at work with more energy than I started with because of regen. I' m guessing regen on the Model S is even better, so I'm not sure I really want to top off completely. It seems like a waste of perfectly good potential energy. Its a short commute, so would charging every other day or so be OK?

No need to overthink this. Just plug in every night for a Standard charge: you'll still have full regen on the way downhill to work.

 

[Hans (Amsterdam)]

@Robert.Boston

This is cycle life. I believe that Tesla Model S standard charge is 4,10V to 3,00V (90% of capacity ?) The chemistry of this cell might different from the one that Tesla uses.
At 600 cycles (standard charges ) still 78% of capacity left. THat would be after approx. 120.000 miles (85kWh) . Of course you have to add the aging effect.



source: http://www.embedded-world.eu/fileadmin/user_upload/pdf/batterie2011/Sonnemann_Panasonic.pdf