Lets look at this a bit differently…
Did you watch the docking of the SpaceX Dragon space ships to the ISS? [https://www.youtube.com/watch?v=xJJhigpMpRo|SpaceX CRS-21 Dragon docking]
Note how it gets close to the station and then comes to a stop at a set distance and then it moves forward as a much slower rate and then when its within a few meters is really gets slow!
Batteries are similar! They can charge at a high rate when discharged more than a third but as the battery gets full the charge rate is dropped and then its at a trickle!
This is all normal!