Energy content of battery by 10% slices

[melmalinowski]

It appears to me that the energy content of my MYLR 2023 is not linear. That is to say, the kWh available from 90% to 80% are greater than the kWh available from 10% to 20%. If this is true, it could answer why the Tesla gets the calculation for predicted remaining battery % on arrival wrong.

I have found that the predicted battery % on arrival gradually declines as you get closer, which makes it risky to try to stretch range down below 10%. As you get closer, it can slide to 5% or less.

This is a problem that could easily be remedied by having a more realistic model of the battery output for each 10%. Does anyone know of a graph that shows the true kWh output across the % content range?

 

[jcanoe]

The displayed battery state of charge (SOC) is an estimate based on the available battery data points such as the open cell voltage (OCV) of the cells in the battery. The Tesla Model Y's battery management system (BMS) can improve the estimated SOC by collecting multiple sets of data about the OCV of the cells in the battery at varying levels of SOC. Periodically operating the Tesla Model Y vehicle over a wide range of SOC, i.e. from above 90% down to below 20% enables the BMS to better estimate the SOC of the battery. If the battery is always maintained within a narrow range of SOC such as 50% to 60% the BMS will not have sufficient data for the battery algorithms to accurately determine SOC. Periodically charge to above 94% so that the BMS can collect data points at the upper end of the SOC of the battery.

The battery OCV measurement can only be performed when the high voltage battery is disconnected from the Tesla Model Y as when in sleep mode. (Sentry mode and Summon Standby prevent the Tesla Model Y from entering sleep mode.) The OCV measurement can take several hours to complete. At home, when possible, leave Sentry mode and Summon Standby disabled so that the OCV measurements can be periodically collected.

The BMS may perform cell balancing after charging has been completed. (Last night I parked my 2020 LRMY with 81% SOC. Unplugged, unlocked, no Sentry mode. This A.M. the displayed SOC was 79%. The lower SOC may have been due to energy used during OCV measurements and/or cell balancing.)

The temperature of the battery pack is also a factor. In cold weather, i.e. below 40F, the Tesla Model Y will begin to lower the estimated SOC. This can be observed by a decrease in resting SOC by as much as -3%.

 

[melmalinowski]

The displayed battery state of charge (SOC) is an estimate based on the available battery data points such as the open cell voltage (OCV) of the cells in the battery. The Tesla Model Y's battery management system (BMS) can improve the estimated SOC by collecting multiple sets of data about the OCV of the cells in the battery at varying levels of SOC. Periodically operating the Tesla Model Y vehicle over a wide range of SOC, i.e. from above 90% down to below 20% enables the BMS to better estimate the SOC of the battery. If the battery is always maintained within a narrow range of SOC such as 50% to 60% the BMS will not have sufficient data for the battery algorithms to accurately determine SOC. Periodically charge to above 94% so that the BMS can collect data points at the upper end of the SOC of the battery.

The battery OCV measurement can only be performed when the high voltage battery is disconnected from the Tesla Model Y as when in sleep mode. (Sentry mode and Summon Standby prevent the Tesla Model Y from entering sleep mode.) The OCV measurement can take several hours to complete. At home, when possible, leave Sentry mode and Summon Standby disabled so that the OCV measurements can be periodically collected.

The BMS may perform cell balancing after charging has been completed. (Last night I parked my 2020 LRMY with 81% SOC. Unplugged, unlocked, no Sentry mode. This A.M. the displayed SOC was 79%. The lower SOC may have been due to energy used during OCV measurements and/or cell balancing.)

The temperature of the battery pack is also a factor. In cold weather, i.e. below 40F, the Tesla Model Y will begin to lower the estimated SOC. This can be observed by a decrease in resting SOC by as much as -3%.

The 'charge above 94% periodically' advice is new to me. Do you have an opinion about whether is good to also periodically charge to 100%, or to discharge to near 0%? Or any other opinions about best charge level for long term storage (say, 6 months)? I've read 50%. Likewise, usage range best for long term battery life (I've read 20% to 80%, or 10% to 60%) A Tesla long-time owner says that 0% is not really zero, that there appears to be a small reserve beyond that, perhaps 20 miles. Likewise what is required to go into what you refer to as 'sleep mode'. I wish Tesla gave an easy way to reliably go into 'sleep mode'. Forgive me if these questions are answered in other threads. I have not seen a good comprehensive post about them.

 

[jcanoe]

The 'charge above 94% periodically' advice is new to me. Do you have an opinion about whether is good to also periodically charge to 100%, or to discharge to near 0%? Or any other opinions about best charge level for long term storage (say, 6 months)? I've read 50%. Likewise, usage range best for long term battery life (I've read 20% to 80%, or 10% to 60%) A Tesla long-time owner says that 0% is not really zero, that there appears to be a small reserve beyond that, perhaps 20 miles. Likewise what is required to go into what you refer to as 'sleep mode'. I wish Tesla gave an easy way to reliably go into 'sleep mode'. Forgive me if these questions are answered in other threads. I have not seen a good comprehensive post about them.

Above 94% or 95% is near the top end of the open cell voltage of the cells in the battery pack. It helps the Tesla battery algorithms if you provide the battery management system with additional data points over a wide range of state of charge SOC. 94% or 95% is close enough to 100% for this purpose. (I occasionally charge to 89% or 90%. I have charged to 94% a number of times but only one time to 100% because I had no need and it takes so much longer including an additional 40 minutes after the display reads 100%.)

The best charge level for long term storage of the Tesla Model Y seems to be 50% SOC. (By contrast, GM engineers provided instructions for storing the Chevrolet Volt for longer than 30 days with the Volt's battery at 30% SOC so who knows.)

The least degradation (loss of capacity) would probably come from maintaining the Tesla Model Y's battery between 50% and 60% with 55% being an average SOC. Most Tesla owners can't or won't care to be this precise with managing the charging of their Tesla Model Y vehicle. Daily or almost daily charging and maintaining the SOC in a range that meets your needs (including the potential need to make an unexpected trip without additional charging before starting the trip.) When it comes to daily charging to 70/80/90% the difference in degradation is relatively small (only a couple of percent.) I prefer to maintain the SOC between 70% and 80%. Sometimes the SOC drops below 70% and other times I end up charging to ~85%.

Higher temperatures, i.e. above 90F (32C), are not good for the long term health of the battery, especially at a high state of charge. Most of us don't have climate controlled parking. The best we can do is park in the shade or underground. (In higher temperatures the Tesla Model Y battery management system may automatically cool the battery pack when the Tesla Model Y is charging or while parked, even when unplugged.)

I would not make a habit of running the battery down to below 10% SOC. A low SOC does not damage the battery (the battery management system (BMS) will always protect the battery by preventing full discharge to occur. The BMS is not able to accurately determine the remaining charge at low levels so you may get stranded. Just because you were able to drive an additional 10 miles with 0% SOC does not mean that this will be the case every time you drive. (10% is approximately 25 to 30 miles of driving.) You may have a tolerance for less reserve range than 25 miles. I like to have a 15% to 20% minimum SOC (approximately 35 miles up to 50 miles) in case of unexpected delays or a Supercharger location that is unavailable.

The Tesla Model Y will automatically enter sleep mode (some say there is even a deep sleep mode) when you park the Tesla Model Y. Sentry mode needs to be set to Off at the location where parked and if you have Full Self Driving then Summon Standby needs to be disabled. When in sleep mode the power drain has been shown to be low (~25W) for the LTE modem, BT modem, door locks and RFID reader for the key card. The vehicle alarm (separate from Sentry mode) is normally active whenever the Tesla Model Y is locked. The vehicle alarm power usage may be factored into the 25W consumption. Contrast this with the ~230W that the Tesla Model Y has been shown to consume when in standby mode and you can see how Sentry mode indirectly results in a ~6 to 7% loss of SOC of the battery over 24 hours. (This equates to close to ~5kWh over a 24 hour period.)

I don't leave my 2020 LRMY plugged in when I am away. I leave my Model Y in my home garage. I know from experience that my Tesla Model Y will lose ~1% per week while parked this way. Due to the frequency of electrical storms (spring and summer) I always unplug electronics whenever there is a forecast for storms or when I am away. This risk is small but the potential for extensive damage to the Tesla Model Y from a close by lightning strike is real.

 

[melmalinowski]

Above 94% or 95% is near the top end of the open cell voltage of the cells in the battery pack. It helps the Tesla battery algorithms if you provide the battery management system with additional data points over a wide range of state of charge SOC. 94% or 95% is close enough to 100% for this purpose. (I occasionally charge to 89% or 90%. I have charged to 94% a number of times but only one time to 100% because I had no need and it takes so much longer including an additional 40 minutes after the display reads 100%.)

The best charge level for long term storage of the Tesla Model Y seems to be 50% SOC. (By contrast, GM engineers provided instructions for storing the Chevrolet Volt for longer than 30 days with the Volt's battery at 30% SOC so who knows.)

The least degradation (loss of capacity) would probably come from maintaining the Tesla Model Y's battery between 50% and 60% with 55% being an average SOC. Most Tesla owners can't or won't care to be this precise with managing the charging of their Tesla Model Y vehicle. Daily or almost daily charging and maintaining the SOC in a range that meets your needs (including the potential need to make an unexpected trip without additional charging before starting the trip.) When it comes to daily charging to 70/80/90% the difference in degradation is relatively small (only a couple of percent.) I prefer to maintain the SOC between 70% and 80%. Sometimes the SOC drops below 70% and other times I end up charging to ~85%.

Higher temperatures, i.e. above 90F (32C), are not good for the long term health of the battery, especially at a high state of charge. Most of us don't have climate controlled parking. The best we can do is park in the shade or underground. (In higher temperatures the Tesla Model Y battery management system may automatically cool the battery pack when the Tesla Model Y is charging or while parked, even when unplugged.)

I would not make a habit of running the battery down to below 10% SOC. A low SOC does not damage the battery (the battery management system (BMS) will always protect the battery by preventing full discharge to occur. The BMS is not able to accurately determine the remaining charge at low levels so you may get stranded. Just because you were able to drive an additional 10 miles with 0% SOC does not mean that this will be the case every time you drive. (10% is approximately 25 to 30 miles of driving.) You may have a tolerance for less reserve range than 25 miles. I like to have a 15% to 20% minimum SOC (approximately 35 miles up to 50 miles) in case of unexpected delays or a Supercharger location that is unavailable.

The Tesla Model Y will automatically enter sleep mode (some say there is even a deep sleep mode) when you park the Tesla Model Y. Sentry mode needs to be set to Off at the location where parked and if you have Full Self Driving then Summon Standby needs to be disabled. When in sleep mode the power drain has been shown to be low (~25W) for the LTE modem, BT modem, door locks and RFID reader for the key card. The vehicle alarm (separate from Sentry mode) is normally active whenever the Tesla Model Y is locked. The vehicle alarm power usage may be factored into the 25W consumption. Contrast this with the ~230W that the Tesla Model Y has been shown to consume when in standby mode and you can see how Sentry mode indirectly results in a ~6 to 7% loss of SOC of the battery over 24 hours. (This equates to close to ~5kWh over a 24 hour period.)

I don't leave my 2020 LRMY plugged in when I am away. I leave my Model Y in my home garage. I know from experience that my Tesla Model Y will lose ~1% per week while parked this way. Due to the frequency of electrical storms (spring and summer) I always unplug electronics whenever there is a forecast for storms or when I am away. This risk is small but the potential for extensive damage to the Tesla Model Y from a close by lightning strike is real.

Thanks, jc. Very interesting. I'm an unusual case, storing the Y in the air on QuickJacks, plugged in for 6 months inside a cool steel building without somone monitoring it (my winters are spent abroad) so not being plugged in is not an option. I wish Tesla provided us with some ability to dehumidify the cabin on a scheduled basis using the heat pump. I have not yet figured out a hack to allow this. I am an iOS programmer, but Tesla only allows a very limited part of the controls to be accessed via their API.

 

[jcanoe]

You could experiment with using Scheduled Departure Preconditioning. This can be set for every day or only weekdays (so 5 out of 7). The cabin would be preconditioned to your preset temperature starting about 20 minutes before the set departure time and then continue for an additional 30 minutes or 45 minutes (I'm not sure how long preconditioning will continue if you don't start driving.) It would use 2% to 3% of the battery state of charge per day (weekdays.)