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If you want to analyze in detail your batteries, ZeroSpy (Android application) can be helpful. It records the parameters of your bike every second. And you can further make graphs in order to analyze the records.
Here is an example with my FXS 2016 (with two 3.3 kWh amovible packs).
https://www.dropbox.com/scl/fi/2qwb24m5nykw2qvnrjkwx/ZeroSpy_modele_analyse.des.donnees.xlsx?rlkey=8or6htwb51w8mqc51jzuq7glo&dl=0
I make a correlation between the balance and the battery current.
You can compare your data to mine.

Another possibility is a change in the firmware way to estimate the SOC.
Here is some of my experience with my FXS 2016.

My old firmware was mainly calculating the SOC from the estimated capacity of the pack in Ah, and the Coulomb counting in Ah. That made the SOC monotonously decreasing, and accurate. Nice !
Indeed, all the logs with this firmware contained lines like
- "Switching to voltage SOC mode"
- "Switching to coulomb couning SOC mode" (there was a typo in the logs: it was written couning instead of counting)

And I am pretty sure also that the new firmware that has been installed is mainly calculating the SOC from the pack voltage, that is greatly oscillating depending on the way you use the bike.
And since this new firmware was installed, there is no line in the logs saying that the SOC mode is using Coulomb counting.

That is why the first thing is to answer if the change in SOC behaviour is correlated with a firmware change or not.
Of course, if the firmware has not been changed, the problem probably comes from the battery.

But it is still not certain. I have also experienced a fundamental change in my bike behavior due to the fact that the MBB had lost all its settings. The most visible consequence was a jump in the odometer (it increased by 3000 kms in one night), and completely wrong odometer count, wrong speeds (all that came from a lost transmission ratio), and also some less visible parameters were lost (pack capacity, VIN number,...). Of course, in that case, the SOC calculation became quite confused also...
Zero reprogrammed the bike and after that it worked fine.

The conclusion is that you should be attentive to anything else that could have changed in the bike (in my case: firmware, and MBB losing its settings).

@dee91
Do you plan to get the "CAN" or the "Enable" version ?
You could be interested by my own experience related here: https://bit.ly/Zero_charger

I agree with Curt. And if you want to take precautions, you can bypass the fuse with another 10A fuse.

https://zeromotorcycles.com/owner-resources
2017 FX
https://prismic-io.s3.amazonaws.com/zero-cms-disco/c55944fa-499e-48e2-83f0-c8dd36657607_OM-XMX-MY17.pdf
Page 6.34, fuse 4, ABC10A, Charge fuse (on-board)

According to
https://zeromanual.com/wiki/Gen2/Regen
and
https://zeromanual.com/wiki/MBB_Console#Settings
it seems that it could be possible to increase the regen.

See for instance the MBB parameter:
maxcustregbrtq  - Max Custom Regen Brake Torque :  10 ( 100 % of allowed )
Custom Mode maximum brake regen setting as a percentage of allowed by the Sevcon controller.

By the way, if somebody has extracted the result of the "set" command from the MBB on a recent Gen2 Zero, with a Login Level greater than the default (0), and listing all the parameters that could be changed, I am really interested by this listing.
 

I have a 2016 FXS and a 2023 S.
I use custom mode, with throttle regen to 0% and brake regen to 100%.
I find the brake regen quite correct on the FXS, and the regenerative braking is sufficient in most situations, if you stay in a quiet driving mode. It uses the Z-Force 75-5 motor with a 420 A controller.
On the other hand, I find the regenerative braking very weak and insufficient on the S, which forces you to brake constantly with the discs, even if you stay in a quiet driving mode. It uses the Z-Force 75-7 motor with a 550 A controller.
I am surprised by some comments in forums or FB, where some S riders find their regenerative braking too strong and have to reduce it using the custom mode.
There are probably some MBB parameters that could be set by a Zero dealer, or by entering the MBB with a higher level than the default one: https://zeromanual.com/wiki/Gen2/Regen . But since the bike is new, I prefer not to change anything myself. Note that the MBB logs with the default Login Level 0 do not give any information about these settings. Moreover there is no competent Zero dealer where I live...

In order to get a quantitative measure of this regenerative braking, I have used the following procedure, that should work with any Gen2 Zero:
- Set the bike in custom mode, with throttle regen to 0% and brake regen to 100%
- Use the ZeroSpy Android application to record the bike data every second
- Go as fast as you can on an empty road and brake using the regenerative brake (and preferably not using the disk, since it would shorten the stopping sequence and you would get less data points on it)
- Do it several times in order to check the repeatability.
- Extract the data from your phone and open the file with a spreadsheet
- Make a column where you multiply the battery voltage by the battery amps, in order to get the battery power
- Make graphs of this battery power versus the bike speed during the regenerative braking sequences
I attach an example. For the FXS I was in town and it was difficult to go faster...
Anyway, it is easily seen that the FXS regenerative braking is more than two times greater than the S one. And the bike is lighter.

If some of you are interested, it would be interesting to draw the same kind of curves in order to see if the regenerative braking differs between bikes and models.
 
And finally the main question is to know if the regenerative braking can be increased by a Zero dealer.

I took the risk to lift the Zero S from the bottom with the scissor jack and it seems to work fine.
Do not forget the rubber spacer that minimizes areas with high pressure.
Images here : https://photos.app.goo.gl/VDmvbjVdWH9VVwEW8