Can I keep the feed wire always into mac? I have read that it damages battery, but other opinion says the present batteries are lithium and I can keep always a feed wire in the computer. How is it in real? Have you any experiences keeping long time the feed wire on mac and what has happened then?

It seems the answer may depend on the particular Mac model and even the OS version, and it sounds like the recommendation may be different depending on those factors -- I would think that's a question best asked of Apple tech support in regard to your specific setup. I don't have a laptop so I can't offer advice from any personal experience..