BATTERY PERCENTAGES NOT MATCHING

[GoodSam]

I believe you need to set your target SOC to 100% for the balancing to work best. Most of the balancing happens when the highest module is above 95% SOC.

Any official or unofficial references to this thought of the need to go to 100%?

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[GoodSam]

Build Date top of sticker inside driver's door b pillar?
@Wonko , @Psmith7279
for my tracking spreadsheet - link in my signature below:

 

[Adventureboy]

Any official or unofficial references to this thought of the need to go to 100%?

It is my understanding there is a technical bulletin supporting the balancing procedure. I do not have the official bulletin however, here are the full unofficial procedures.

Procedure (NMC packs):

1. Charge the vehicle to your normal level (e.g. 90%).
2. Drive the vehicle (without charging) until the battery is down to 5% or less.
3. Park the vehicle and let the battery rest for at least 5 hours (preferably overnight)
4. Level 2 charge all the way to 100% in one session without interruption.
5. Leave the vehicle plugged in and let the battery rest for 3+ hours after 100% is reached.
6. (Optional) With a scan tool, read the kWh to empty and state of health parameters.
7. Drive without charging until battery is below 50% (10% recommended)
8. Charge the vehicle back up to your normal level.
9. Repeat if desired.

The OP has had a battery module replaced so it may take more than one iteration of the procedure above to balance the pack.

Balancing is more important for LFP batteries, but it is still needed on NMC batteries occasionally. Try this - watch your charge when you get to 99% and see how long it takes to get from 99% to 100%. This is where the bulk of the balancing happens and if you haven't done it for a while, it can take several hours to bring all modules and each individual cell to full 100% SOC and actually show 100% SOC on the gauge.

Nearly 2 years on my 2023 Lightning ER and my pack SOH is still 100% so the monthly 100% SOC charge is working. I have also built my own LFP packs and configured the BMS myself so I have a pretty good understanding of how they work. It is very difficult to balance the cells/modules below true 90% SOC due to the very low voltage difference below that. Ford protects the top 7-8% SOC so we need to be at 100% gauge SOC for the balancing to work effectively. The top balance is needed for all Lithium battery chemistries occasionally.

 

[Adventureboy]

I never hit 100% until I pulled the charge cable and started the truck up.

It can take up to 3 hours or even longer to go from 99% to 100% as it balances all cells/modules.

 

[TaxmanHog]

It can take up to 3 hours or even longer to go from 99% to 100% as it balances all cells/modules.

Sorry for confusing the discussion about getting a pack back in line, vs. an occasional charge to 100% that is otherwise healthy.

I was not aware of the details outlined in post 18.

 

[Jim Lewis]

While looking around for other info on balancing, I came across this interesting opinion:

If the pack is out of balance, the effect is a temporary loss of capacity: when charging, you have to stop when the most highly-charged cell group hits the maximum allowable voltage, and when discharging you have to stop when the most lowly-charged cell group hits the minimum allowable voltage (in either case the cells would be damaged if you didn't stop).

....

The main impact of never balancing is that it will take a very long time to balance when you do eventually get around to it. If you are never balancing, then presumably you are never needing 100% of capacity, so the fact that you've lost access to it doesn't really matter.

Source: Battery balancing — what's it for? | Speak EV - Electric Car Forums

The other interesting thing I learned is a need to balance cells arises from frequently charging and discharging the battery, the more so if you venture into the highs or lows of the battery % SOC range. Chronological battery aging can also slowly generate a need to balance cells. I also read somewhere that cells will degrade faster if they're out of balance.

There seems to be an alternative opinion on the Internet that Ford, especially since it doesn't mention any need for owner intervention, service interval adjustments, or charging to 100%, has built self-balancing during normal charging into its BMS. It's said in more upscale EVs, self-balancing is often a BMS feature. So, perhaps the question is then, how upscale is the Lightning?

 

[Adventureboy]

has built self-balancing during normal charging into its BMS.

Ford will have balancing built in through the full SOC range but the challenge is simple physics. In the mid-SOC range, the voltage difference between the high cells and the low cells is very small so only a very small amount of balancing can be done in the mid-SOC range. As the cells pass the "knees" in the voltage range as they approach the upper SOC values, the voltage difference is much greater between the high and low cells making balancing much more effective.

In a perfect world, all cells would be identical. The reality is quite different. Example: two identical cells roll off the production line with identical specifications. Once cell is installed in the centre of the pack, the 2nd cell is installed near the outside of the pack. Simple temperature differences during the operation of these two identical cells will cause them to diverge over time and become out of sync. Balancing brings them back in sync.

There is no need to be religious about charging to 100% monthly with NMC. Once every month or two is healthy for your pack especially if you live in temperature extreme climates or you use the giddy-up lots. If you have had your truck for 2-3 years and have never charged to 100%, you aren't doing it any favours ;-)

 

[Jim Lewis]

If you have had your truck for 2-3 years and have never charged to 100%, you aren't doing it any favours ;-)

My truck only has 3,900 miles, and according to OBDLink, with an OBDLink MX+ scanner, there is a 0.0% voltage difference between cells and a 0.6% charge difference. I vaguely remember reading quite a while ago in another thread that if there is no voltage difference between cells and less than something like a 1% charge difference, there is no need to rebalance. I wonder how often our resident battery expert @MickeyAO balances his truck cells? But then he probably drives a whole bunch more than I do. And I wonder, post-retirement, whether he is allowed to disclose anything he might know about the degree to which the Lightning BMS can self-balance. That would seem to be something worth looking into when dissecting the battery system performance of an EV.

My truck is also kept in an insulated garage, and I rarely let it sit out in a hot parking lot in San Antonio during the summer. The battery usually doesn't drop more than 5% SOC on a few short daily drives, and it's always charged to 50% every night. The truck is leading a pampered, idle life.

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