Battery won't fit the track :(

I have an ebike with a small 15 ah battery so I bought a second battery but the problem is that it won't fit in the track of the original battery :( and the thing is I can't take the other track out because it is connected to controller. What do I do should I sell the battery or maybe there is some way to do it ? And the battery that I bought doesn't have any cables it either fits in or not. Is there any way maybe to fix this or do I get rid of this battery ?