Macworld A Macworld reader has a perfectly good 2009 MacBook Pro–except for its swollen lithium-ion battery. He wants to keep it on hand for limited uses after safely removing and disposing of the battery. Is there a downside to working battery-free? Not really. As long as you’re always plugged in, a Mac laptop has no idea about or interest in whether it’s drawing power from a battery or a wall outlet. Years ago, I used a hand-me-down iBook like this (in the era in which you could just pop out a dead battery, as they were removable) so my kids had a machine to work on when they were little. Of…