I'm not sure under what conditions you are considering a permanent trickle.
Charging in any case will only be happening when the battery is low - say from sitting around and having lost charge, after operating electronics on the ground without the engine running without an external supply, and particularly right after a start, when a significant chunk of energy has been drawn from the battery. With the engine running, the regulator takes the sensed voltage and shoves field current into the alternator to produce whatever current is necessary to push the sense voltage back up to the regulation point, however that is set. Strictly speaking, it isn't exactly like that, as there is some elasticity built in, there are rpm and alternator capacity limits that come into play, etc. Again, steady state in flight, the battery is not charging at all - the alternator simply supplies all the load current exactly. In any case, the regulator does not see or have any direct knowledge of the alternator output current, which ultimately gets determined by the battery characteristics, specifically its effective series resistance, as well as the overall battery circuit resistance, including the cables to the battery. Lithium batteries in particular have lower internal resistance and therefore are know for higher re-charging currents after starts.
Now, if you are talking about the application of an external trickle charger for example to keep the battery full when flown infrequently, yes, steady state trickle chargers are not good for any batteries as they will lead to overcharging and generally irreversible chemical damage, reducing life expectancy. But, there are special chargers for storage applications that circumvent this with a variety of pulse and intermittent charging techniques, such as those made by a company called Battery Tender. I have one on a car I store through winter in the hanger, and it works great.