overheating fuse housing

I am new to this site and I hope maybe someone can help with this problem involving an E-Xtenzo Chinese 350 watt 48 volt small scooter I bought online. I have been using it for the past few months with no problems but recently noticed the fuse housing which is attached to the battery case had gotten so hot it had melted the plastic it is connected to. The scooter still runs fine and charges up with no problem. It had a 30 amp fuse which seemed awfully big and I changed to a 15 amp fuse but the fuse has never blown. I don't have any specs on the bike which makes things a little more challenging. Any ideas what cold be causing this load to the fuse circuit? The fuse is part of the 4 battery wiring circuit and can be removed with the battery pack.