My understanding of AGM vs flooded lead acid (FLA) batteries is that FLAs like to gas/outgas but AGMs do not. It is pretty much a requirement to increase the charge voltage of FLAs so that they gas and "de-stratify". However for AGMs, that is not a requirement, nor is it recommended.
So my idea is for AGMs, if you are not in a hurry to charge them, why not just set them at the trickle charge voltage and let them slowly charge (such as overnight)? An example would be I used my battery bank during the day and it is resting at 12.3V (a mid state of charge for AGM). Now suppose I have a 13.6V 10A power supply (ps) and just connect it to the battery for many hours. In theory, I don't have to worry about overcharging the battery since 13.6 is already the battery manufacturer recommended trickle charge / maintain voltage.
I have also tried this method with Lithium Iron Phosphate batteries, setting the charge voltage to 14.2V and watching the charge current eventually drop to 0.000A.
For AGMs and LiFePO4 (LFP) batteries, it seems like a good safe technique since you are guaranteed not to overcharge the batteries and it is healthy for AGMs to keep the charge voltage lower so there will be no loss of water.
So my question is are there any drawbacks (other than slower charge times) for using this method? What might it do to the life of the battery charging it ONLY this way?