My Air's charger works only when it wants to and totally randomly, and since it's out of warranty I have to buy a new one. I read somewhere that Mac chargers auto-detect which laptop model you're connecting and regulate the Watts accordingly, so I was wondering, since they all cost the same, if it was better to get the 85W charger instead of the 45W that comes with the Air. Are there any downsides? Is it bigger? Thanks for the help!