Reason for me raising the case was two fold:
1) On my system (10kW inverter, 12.8kWh battery), it looked a little strange that 50% charge rate gave 5Kw charge power and 100% charge rate gave 6kW charge power, due to the limited charge power allowed by the battery. But this is not that essential, just a strange charge curve;-)
2) WW charged with a higher power that necessary, thereby nor utilizing the whole charge period.
I believe, that "Low and slow" is best for batteries (along with not utilizing extremes like 0% or 100% for longer periods. And I thought, that WW could be optimized with respect to battery life by taking into account the maximum charge rate possible for a given battery. This said, I have not found any scientific sources with relevant information regarding this.
By the way, I found out, that Growatt limit discharge to 10%. It is not user kontrollabel and they will not guarantee battery life if changed. So, I paid for 12.8 kWh and got 11.5kWh.
Thank You, Admin, for taking the time to improve WW on this topic, I'll try it out a few days and report back with the results.