I am also considering Lithiums for 36V Trolling motor, 3x 100Ah. My biggest deciding factor is to go with a cheaper $350 or $800 battery. There are many good tear downs on batteries at this link and if you go over to BBC there are dozens of discussions on Lithium batteries.
Depending on your current charger, you may be able to have it reprogrammed versus replacing. For my Dual Pro 4x15A, the cost to reprogram is about $180 plus shipping.
If you have a switch in your boat to allow for switching over to one of the trolling motor batteries from starting battery, when going to lithium this is probably going to be a problem as most lithiums can’t be used for cranking.