A few days ago when I tried to recharge my Wii remotes, I found that after 15 minutes or so the red charging light on the station would flash and my remotes wouldn't charge. I tried placing the Wii remotes on the other pad and switching out the charging units, but nothing was happening. So I then decided to try replacing the batteries inside of the battery packs, and that worked like a charm! You can either buy a new battery pack, or just unscrew the pack and replace the two green batteries with rechargeable AAA batteries from the store (which is cheaper and more convenient).
Hope this helps anyone else who has this problem!