The 208 has a rather simple battery/switch layout and some of the suggestions listed may be overkill. There isn't a lot of potential house load for the base model 208,other than GPS, VHF and maybe a stereo. The 208 is also only a single motor hull.
You can run everything on one battery and keep the second as backup. The idea of a charger at the dock sounds like a good idea but in the 15 years I have had my 208, I have never charged at the dock. For winter storage I make sure that both batteries are fully charged before disconnecting the grounds for the winter. I get about 7 seasons out of my batteries but granted don't run a lot of load.
I do tend to alternate which battery I use each trip and that does a few things: If a battery is getting weak, I will know before it's too late. Both batteries also get charged alternately.. For the most part, I never go out on the BOTH setting but if the return trip is 20 minutes or more, I often select BOTH on that return trip to give a charge to both batteries. ( Remember not to turn the battery selector past OFF while the motor is running. Passing the BOTH position is OK
For optimum longevity, especially if you like to run on BOTH, your batteries should be the same size, brand, type and age. Bottom line, they generally both should be replaced at the same time.