Mine stopped working after a week (light on the charger was in, but not charging the battery). The store wapped it for me. My replacement has been trouble free for a month. Fingers crossed it stays that way ☺
I had a similar problem with my SP1 charger.
Seems to be many problems with the MS chargers.
I'm not sure if MS have QC issues, or they just don't have the experience yet to design reliable / durable hardware.