Regenerative braking - why does the maximum strength vary?

EV drivers, have you ever noticed that your regen braking doesn't seem as powerful as usual just after you have fully charged your battery?

My wife was surprised by this yesterday when we went into town, just after I had finished charging to 100% at home.

The reason is the same as why the charge rate slows down as you approach 100% state of charge (SOC) when charging.

Lithium (also Lead-acid) batteries have a bulk stage of charging where maximum available current and power can be fed to the battery, while the voltage increases. Once the maximum battery voltage is reached, the current (and power albeit now at constant voltage), must be reduced to prevent this voltage being exceeded, which could otherwise result in battery damage (think of the results of cheap e-scooter chargers!). This is commonly called the absorption stage of charging, where the charge controller reduces the current supplied to the battery. As the battery nears full, even with a 350kW supercharger, the charging power will drop to a level comparable with a home charger.

Regenerative braking can put many tens of kilowatts of power into a battery, which is fine once the battery SOC is well down from maximum, but when the battery is near fully charged this amount of regen must be limited in order to protect the battery. The expected level of deceleration is absent, so if you are accustomed to one pedal driving, you'll need to wear down your brake pads a bit to slow down.