Battery Switches while at anchor...

[scooper321]

One more thing: if your batteries were dead after 5 days, replace them. They are shot. Assuming you have no electrical problems (unknown shorts, for example) the stereo “memory” and other DC loads will not drain batteries in weeks, much less 5 days. If yours died that quickly, your batteries are at their end of life.

 

[JVM225]

When I had a twin engine boat with no generator I would shut off one of the two banks when I got to where I was going (anchorage or transient dock for a few hours) and leave the other one on for lights, radio, fridge, etc. just in case I killed the batteries on that bank I could employ the emergency start.
Now that I have a boat with a generator I just leave both the port and starboard banks on. Generator has its own battery.