Winter Sux wrote:
Either or on the + and - but just remember if disconnecting the +, when the other battery is still hooked up if the battery switch is on, the + cable is live and if it touches any part of the block and most metal things, ZAP! This can fry electronics.
I go to the trouble of taking mine out for the winter and trickle charge them once a month and keep them off concrete. Also, IF one short circuits internally, the specific gravity will drop enough they can freeze and crack the case. Come spring, you'll have an acid mess to clean up. A bit of overkill Mike but I'd rather be safer than sorry.
John

The above is true!! But remember too, if the POS side is disconnected & a pos wire from a pump or anything hits the pos post, it will/could turn on. Now let say a neg wire from anything is grounded and hits the POS post. It will short out and pop a fuse, kill the battery, burn up a wire and so on. If the Neg side is off the battery, Most loose wires in the winter/storage are POS, with that said, if the wire hits ether post of the battery, nothing will happen. Same holds true if a small neg wire hits ether post.
Now anything could happen, but in general, it is safer to remove the NEG side off the battery.
I do remove both and leave the batteries in the boat over the winter. There AGM type, so they will not frezze and hold there charge over the winter.