I have been shutting the batteries off after each time I use the boat. Is this overkill? Will the batteries be to low not to start the boat after a week of not using it?
Leaving it on for a week should be no problem if your battery is in good shape. The radio memory should be a very small drain, especially compaired with all the devices the average car or truck has nowadays, and they can typically go for weeks and still start.
I have the small solar trickle charger with regulator control to prevent overcharge. It is hooked up all the time and keeps the batteries fully charged. I have used these for many years and had no issues with the batteries. You can get the panel and charger very inexpensive from harbor freight. I have never had one fail yet.
I am a Battery Tender guy, too many cars and motorcycles and now a Bennington to not have things plugged in. I actually had an A/C Delco factory battery last 7 years keeping it plugged in. (And those are not the best batteries to begin with)
I turn my battery switch off, dual battery set up, and I always alternate between switch position 1& 2 as Odd/Even date usage. Using two Tenders now waiting for one to die (or to purchase another toy) because I have my eye on one of their Dual port 12 volt chargers it is currently on Amazon for about $81,,, Just to provide a clean install in the battery compartment and a single plug in to the extension cord when the boat goes up on the lift.
Take care of those batteries and they take care of you. jus saying