Rechargeable batteries not charging

I found an old Kodak Easyshare Z712 IS camera. It came with an in-package kodak rechargeable battery supply. I put the battery in and was able to take pictures for about 20 minutes before they died. I purchased a charger for the camera on ebay. The camera will run with the charger plugged in, but when it is removed the camera turns off. The camera will run on the charger even if the battery pack is removed. I also tried normal AA batteries and the camera will run on those. The charger does not seem to be charging the batteries, is there anything I can do?