I hit a similar issue with an iPad today - there is no easy way to tell if it is charging slowly.
It was showing the charging icon, although only charging at 1W. Horrific UI. I changed cables, it was charging at 5W. Shit, the charger was a 5W charger for an iPod (charger looks the same, need to read tiny low contrast writing to tell difference). Changed to a 10W charger, now charging at 7.5W. Change to another cable, finally 10W.
Fortunately I had an in-line USB diagnosis tool (about $10, google for USB power meter) otherwise you are screwed trying to diagnose why your iPad seems to be charging slow...
It was showing the charging icon, although only charging at 1W. Horrific UI. I changed cables, it was charging at 5W. Shit, the charger was a 5W charger for an iPod (charger looks the same, need to read tiny low contrast writing to tell difference). Changed to a 10W charger, now charging at 7.5W. Change to another cable, finally 10W.
Fortunately I had an in-line USB diagnosis tool (about $10, google for USB power meter) otherwise you are screwed trying to diagnose why your iPad seems to be charging slow...