what brand 12V do you guys recommend?
I've used Interstate Batteries and the Batteries from Walmart. They are relatively competitive and if you keep them topped off and charged, then you shouldn't have a problem.
What recharger to you recommend?
My boat has two batteries for the trolling motor and another two batteries for accessories and cranking the engine. The trolling motor batteries are hooked to a dual bank charger that I got at Sportsman's. I don't remember the exact name but I keep it plugged into the wall when I'm not using the boat and I have a habit of selecting the battery re-condition option about 24 hours before taking the boat out.
I was getting frustrated with killing the cranking battery after trolling so I did some customization on the non-trolling motor boat batteries. I have one cranking battery that is connected to the motor (starting and lowering/raising the motor) and because I was having trouble killing the cranking battery while running live wells, radios, lights, trolling, etc., I bought an isolator from Hellroaring Technologies http://www.hellroaring.com/
and isolated a deep cycle battery through the cranking battery. When I'm running the boat (or charging the cranking battery) the cranking battery gets charged as a priority. Once that battery is charged, then the isolator kicks on and charges the deep cylce that runs everything else. If I kill the deep cycle, I still have a cranking battery because it's isolated. All I have to do, is run the motor until it is recharged. If I kill the cranking battery, the isolator will kick on and give me the power to automatically "jump start" the cranking battery.
I have a conditioning charger at home that I connect to the cranking battery. Again, once this battery is charged, the isolator switches on and charges the deep cycle.
One important thing to note - There is a difference between a conditioning charger and a trickle charger. Conditioning (automatic) chargers are less expensive. Problem is, if that battery has less than 4v (I think that's the level) left in it, the automatic conditioning charger will not charge it. You will need to use a trickle charger to charge the battery up to the minimum, then connect the conditioning charger. If you don't leave your batteries connected to a conditioning charger in the winter, your batteries will die to the point where you will need a trickle charger first. Additionally, you don't want to leave the trickle charger without the conditioning feature plugged in all the time.
How often do I have to change the batteries?
I've had all 4 batteries for 4 years and haven't had a problem (yet).
Will a regular car battery do the job for the electric trolling motor?
Use a deep cycle battery for this as has been advised by others.