I have a Bass Pro Shops "Grizzly" 16' aluminum boat. I want to put a new 25 hp Yamaha tiller, electric start on the back. At this time I have two group 24 battery's hooked up in the rear of my boat to supply my 24 volt bow mount trolling motor. The only thing I have on these battery's in addition to my trolling motor are two "cheap" depth finders. I really do not want to add the weight of another battery in my boat if I do not have to. So my question is can I hook this motor directly to one side of my trolling motor battery set-up?
Thanks for your help.

Yes, your motor should have its own dedicated battery. Your Yamaha is 12 volts. Connecting it to one battery that is connected to another in the 24 volt system could send a strange load to the computer in your motor that could fry it.  Your depth finder shouldn't be connected to the trolling motor batteries anyway.

I never gave a thought to the motor being 12 volt, hooking up to two batteries in series going to a 24 volt TM. Interesting.

Thanks for your thoughts.

Yes, you do need another battery. The only thing running off your TM batteries should be your TM. Never run anything else off them as it will cause one to deteriorate quicker thus lowering the actual battery you have. Run your motor and electronics off a dedicated cranking battery and leave your TM on their own batteries.