Those appear to be the Silverfish case, which has been around for a decade or more. I think it's a robust aluminum case, although top/bottom are plastic,
The height can vary because they make the case longer for higher cell count. A different height affects the location of the round hole in that rear locking strip, but that has some adjustment. They often include a new strip with a battery, and your bike appears to have room for a taller battery,
You also have to worry about the number of pins (five) and their polarity, but that's easily fixed by flipping the contacts.
It's the cross section that must be your problem., I have an old one here, 111 x 77 mm. I think that's standard. You might have to look for the smaller ones direct from China,
I have an old case by my desk and the cross section is 111 x 77 mm, probably the standard size. Here's a smaller one. sold by the
dreaded Unit Pack power in China. Everyone hates them. I;ve bought five of their batteries. Four have premium samsung cells and have been working for years, The fifth wore out after 5 years. It still worked, but only had half its capacity., I would contact them and ask for a price with premium cells.
