I have dual batteries with a switch and two posts under the rear seat.
I want to hook up a battery tender for the winter.

Where do I connect it?

Not sure if the posts by the switch under the seat are direct to the batteries or just to power the hatch if batteries go dead. It's an 07 Baja Outlaw.

I take mine out. Keep them nice and warm in my garage with the tenders hooked up.

Get a Guest 2611 10 amp 5 per bank onboard charger and forget about any battery problems!

disconnect batteries and use a tender for each one or switch them around every two months

x2... didn't buy a Guest, but got a dual bank marine battery tender/charger. Plug it in, forget about it. Good to go on the next trip out.

I always just take them out for the winter, put them somewhere warm. then in the spring put them both on a charger. they don't loose much charge if any just sitting for a couple months.

I use the batter tender. Probobly not the recommend way of doing it, but for the past 10 years I've always just hooked them straight up to the battery without disconnecting the battery from the boat. For twin batteries I use two battery tenders, thats it. I've done it with the sea ray since new (04) and on the 28 apache. No problems, and it doesn't seem to have any impact on the life of the battery. One time when the battery went dead the tender burned up (not literally) trying to charge it up. I try to keep the tender away from anything flammable. If the battery goes dead it will warm up a bit trying to keep it charged, but not enough to cause damage.

Thanks guys. At the risk of sounding lazy..... I would like to leave the batteries in the boat if possible. Want it ready to rock and roll at all times.
There's no way to use one tender to charge both batteries simultaneously?

The battery tenders are ok, but not the best.

The battery tenders float the battery at a voltage, in essence equalizing all of the cells low. So if some cells are lower than others, those cells can sulfate. If you do want to go the battery tender route, that is fine, however once a month you need to raise the voltage to equalize the cells. Put on a good charger for a few hours should do it.

The better charges mentioned should do it automatically, or there should be a button/contact on them to make them go into "boost".

All batteries will drain minimum 5% every month with nothing connected. All the battery tender does is equalize that drain, it is not a charger. By charger, I don't mean 10 dollar wallmart special. You really need to spend some cash on a high rated charger to keep your batteries in perfect condition. They do more than just charge. We sell battery charges in the power industry to generator OEM's.

Sure. Leave your switch in the both position and hook it up to either battery.