Mach-Lee
Well-Known Member
- First Name
- Lee
- Joined
- Jul 16, 2021
- Threads
- 207
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- 7,853
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- 15,771
- Location
- Wisconsin
- Vehicles
- 2022 Mach-E Premium AWD
- Occupation
- Sci/Eng
- Thread starter
- #1
First, let me say this is somewhat controversial, as there is no official procedure from Ford for this. However I think it helps to do this periodically, especially in vehicles that don't get the pack exercised very regularly. As in most of my articles, nerd content warning applies here, just focus on the procedure below if you aren't one.
Background: Like virtually all lithium-ion battery systems, the Mach-E uses a battery management system (BMS) to estimate the amount of energy in the battery pack, which is used to display the state of charge % and the range. The system does a pretty good job, but over time the calibration of the BMS can drift, especially in vehicles where the battery is always kept in the middle of the range (which is good battery practice). This can cause the capacity estimate to become more inaccurate with time, which affects the displayed % and range. Most BMS systems are programmed to be conservative, which means the capacity and range is typically underreported when the BMS has drifted. Similar battery calibration procedures have been successful in improving range estimates in other EVs such as Teslas.
Please Note: The displayed range on the Mach-E GOM is heavily affected by driving habits and outdoor temp, BMS calibration is a much smaller factor compared to these. Do not do this just because your range dropped suddenly, that's almost certainly because the outdoor temp decreased and calibration will not help that. Range drop due to temps below 55ºF is perfectly normal has been well documented elsewhere on the forum.
Benefit: You may see a 1-6% capacity/range indication improvement (not verified or guaranteed) after a BMS calibration.
It's important to understand that performing a BMS calibration does not physically restore lost battery capacity (which is gone forever), it merely updates the computer estimate of capacity only so that it is more accurate. The battery has whatever intrinsic capacity is currently has regardless of what anyone says, does, or thinks (including the GOM), so you could argue it's best to not think about BMS drift and just go about life unless you are concerned with accuracy.
Disadvantage: Performing a battery calibration involves pushing the pack to extreme states of charge, which can degrade it very slightly each time. Therefore you should only perform this procedure sparingly. If you are ultra-concerned about your battery health and feel like you have plenty of range, then don't do this.
I recommend you perform this procedure every 6 months, especially if you never charge to 100%. Every spring and fall is a good time. It's not necessary if you take regular trips where you hit extremes of charge.
Procedure:
More Background: The BMS assumes the average user will charge up to 100% occasionally for trips, and also drains the battery below 20% periodically. When this doesn't occur regularly, the BMS drift can increase due to the very flat nature of the lithium discharge curve (see below figure). It's very difficult to estimate the actual state of charge in the 20-50% region, it could be off by upwards of 10% based off voltage alone. The BMS employs coulomb counting (via a current sensor) to improve the accuracy here, but that's the aspect most affected by drift since small errors in current measurement accumulate over time. Therefore spending some time above 90% and below 10% where the voltage curve has the greatest slope is important for the BMS to get a good read on the battery SoC. Some cell balancing will also occur during the rest periods at high and low SoC, which improves the estimates of total pack capacity.
Last, a reminder that outside of calibration and trips, it's good practice to always keep the battery between 20-90% for maximum longevity, and charge to the lowest level you need for everyday use. Users that follow good charging practices actually have the most need to do a battery calibration periodically as explained above.
Background: Like virtually all lithium-ion battery systems, the Mach-E uses a battery management system (BMS) to estimate the amount of energy in the battery pack, which is used to display the state of charge % and the range. The system does a pretty good job, but over time the calibration of the BMS can drift, especially in vehicles where the battery is always kept in the middle of the range (which is good battery practice). This can cause the capacity estimate to become more inaccurate with time, which affects the displayed % and range. Most BMS systems are programmed to be conservative, which means the capacity and range is typically underreported when the BMS has drifted. Similar battery calibration procedures have been successful in improving range estimates in other EVs such as Teslas.
Please Note: The displayed range on the Mach-E GOM is heavily affected by driving habits and outdoor temp, BMS calibration is a much smaller factor compared to these. Do not do this just because your range dropped suddenly, that's almost certainly because the outdoor temp decreased and calibration will not help that. Range drop due to temps below 55ºF is perfectly normal has been well documented elsewhere on the forum.
Benefit: You may see a 1-6% capacity/range indication improvement (not verified or guaranteed) after a BMS calibration.
It's important to understand that performing a BMS calibration does not physically restore lost battery capacity (which is gone forever), it merely updates the computer estimate of capacity only so that it is more accurate. The battery has whatever intrinsic capacity is currently has regardless of what anyone says, does, or thinks (including the GOM), so you could argue it's best to not think about BMS drift and just go about life unless you are concerned with accuracy.
Disadvantage: Performing a battery calibration involves pushing the pack to extreme states of charge, which can degrade it very slightly each time. Therefore you should only perform this procedure sparingly. If you are ultra-concerned about your battery health and feel like you have plenty of range, then don't do this.
I recommend you perform this procedure every 6 months, especially if you never charge to 100%. Every spring and fall is a good time. It's not necessary if you take regular trips where you hit extremes of charge.
Procedure:
- Charge the vehicle to your normal level (e.g. 90%).
- Drive the vehicle until the battery is down to 10% or less.
- Park the vehicle and let the battery rest for at least 5 hours (preferably overnight)
- Level 2 charge all the way to 100% in one session without interruption.
- Leave the vehicle plugged in and let the battery rest for 2 hours after 100% is reached.
- (Optional) With a scan tool, read the kWh to empty and state of health parameters.
- Drive without charging until battery is below 50% (10-20% recommended)
- Charge the vehicle back up to your normal level.
More Background: The BMS assumes the average user will charge up to 100% occasionally for trips, and also drains the battery below 20% periodically. When this doesn't occur regularly, the BMS drift can increase due to the very flat nature of the lithium discharge curve (see below figure). It's very difficult to estimate the actual state of charge in the 20-50% region, it could be off by upwards of 10% based off voltage alone. The BMS employs coulomb counting (via a current sensor) to improve the accuracy here, but that's the aspect most affected by drift since small errors in current measurement accumulate over time. Therefore spending some time above 90% and below 10% where the voltage curve has the greatest slope is important for the BMS to get a good read on the battery SoC. Some cell balancing will also occur during the rest periods at high and low SoC, which improves the estimates of total pack capacity.
Last, a reminder that outside of calibration and trips, it's good practice to always keep the battery between 20-90% for maximum longevity, and charge to the lowest level you need for everyday use. Users that follow good charging practices actually have the most need to do a battery calibration periodically as explained above.
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Last edited:
Items 4 through 8 sounds like my daily routine. Well, pretty close anyway. Most days I get back home with around 60% remaining but some days it is 30-40% but that only happens 2-3 times per month.
