After a very frustrating season last year with a flaky, old 5hp on my converted 16' semi-v, I decided to go all electric (our lakes aren't electric only, but they are fairly small [under 400 acres mostly] and I like the reliability).  Two days ago I scored a lightly used Maxxum 74t for the back of the boat for only $138.  However, this is my first 24v, so I have a couple questions.  

1. What kind of battery life can i expect from 2 29series batteries with the 74t?  It has the maximizer technology.

2. When I wire the batteries, I connect the +/- of the batts together and then connect the motor wires to the remaining unused +/- terminals.  That I get, but if I want to run a fishfinder from the setup too, do I connect it to the inner +/- terminals that are connected to one another in order to get 12v?   Thanks.

If you are not hooking it to the start battery of the boat the just hook it to one of the batteries + to + and Neg to Neg doesn't matter which one.

Yes your ff goes to one battery only.  As for the 29 series batteries they should be worlds of juice.  Do you know how many reserve amps (reserve capacity) they have?

They are the Wal Mart Everstart MAXX 29 series batteries.  the 74t will be the main propulsion, so I'm just trying to get a feel for my range.

I can fish 2 days with my two 27 series everstarts on one charge.  And that's pulling around a 21 ft stratos.