Every once in a while, my Magsafe won't charge my mac. The LED stays green, goes out completely, or remains lit only faintly and it sends little or no charge to the battery. This happens intermittently.
All the lights light correctly and the Mac battery receives a charge when I plug in someone else's adapter, so the problem is not my Mac.
My Magsafe adapter works correctly when plugged into someone else's computer (all the lights) so the problem is also not my adapter.
I have a friend who has the same problem, and when it happens we can trade adapters for a while and it seems to fix the issue. I'd love to hear a technical explanation of what might be going on from someone familiar with how these batteries and chargers interact.
Not sure why over all these years they haven't made that a replaceable component, but it is the cause of failure of many an expensive power supply. Stings even more when even Apple compatible AC adapters are in the $50 range.