I agree with you, double up on the charts, I did for my Lowrance too, I have the HDS units linked together and with the Garmin on the console, I use it to get me to the spots and then I can fine tune on the Lowarnce. When fine tunig areas, I don't really need the maps but they do give a better reference association on where you are.
My 276C has lost it's internal over a year ago. I simply turn unit on on my way out the door, plug it in the cig lighter, by the time I am at the lake, it is locked in and ready to go. I also use my garmin for navigating in the truck.
Too bad you can't link Garmin and Lowrance together.....
Cheers, Ron...