Gba sp AGS-101 charging problems

Hello I recently bout a refurbished gba sp AGS-101 off eBay and it isn't charging correctly what's happening is when I put it on the charge the amber charge light comes on and it doesn't go out even after 18 hours of charging and the battery only lasts for about 2.5 hours at best can someone please tell me what is wrong also I have tried 2 different brand new batteries in it