The electric putty is the best install period. You don't need the foam block. John was starting a different install when Lunchbox and I told him about the putty install.
Take a 2" ball of the putty and work the air out a bit. Stick the ball to your transducer. Locate your desired install area and smoosh it down. That's all there is to it. Where depends on what type of kayak you are installing it on. If it's a Hobie, make sure you are forward of the Mirage Drive near the hull mast.
Make sure that the entire face of your transducer is covered in putty and that the transducer is parallel to the hull. You only need an 1/8 1/4 of putty in between your transducer and your hull.
As for the battery, throw away the 8 AA pack if one came with the unit. They work fine, but are far from ideal. Most people prefer a 12 volt 7 amp hour battery. I buy mine from Ebay and for far cheaper than you can find it in stores. Even after shipping costs. I fish on average 3 days per week and only charge my battery every few weeks. When I used the 8 AA pack, the batteries would last 8-10 hours. When you do the math, you'll find the brick battery to be WAY cheaper at $15-$20.
Hope this helps