Cant say I agree with using a diode pack, They are generally used on bigger boats with different alternators to that found in an outboard. Also they are quite big and not waterproof, so fitting can be awkward.
I prefere the line that using two batteries that are entirely seperate from each other, except for the change over switch, allows one to quickly change to the other battery in the evnt of a failure. Never use the both setting, as a fault somewhere could leave both batteries flat!
I employ the regime of Saturdays, Mondays, Wednesdays and Fridays I use battery 1 and the other days I use battery 2. This ensures each battery gets charged up.
Indeed I had a charging problem in mid channel this year. Switched over to the other battery and it got me home. If I had been running in both mode, I would have had 2 flat batteries and a long tow home.
Searider - The Best 5.4 x Far