I think you need to be a member of thier online club to get the price, but this comes with a 3 year REPLACEMENT warranty. I use this to keep the jeep battery 'warm' and you can find quick disconnects to you can simply plug it into the pigtail. Works wonders for winter storage.
It lists for $29.99 but online has a $10 off discount, so its $19.99... but online only. Walk into the Sears store and its $29.99