Went to battery plus the other night to pick up a watch battery. While I was waiting, they had a huge stand of X2 automotive batteries. The only thing the sales guys knew was they have a 5 year warranty, they are heavy as crap, and he was pretty sure they are Northstar rebranded. I have gone online and dont find much other than ads. Are these really good? Good enough to justify the 300 buck and over price depending on size? I guess how would these compare to an XS battery?