Ok so I'm in the process of doing a Gsxr tail swap on my gen 1 and I ran into a problem the battery's I have are way too big to fit anywhere in the tail. Can I get a smaller battery and how small can I go?
Yes, you can get a smaller one. I would recommend a Shorai.
The stock battery on an SV appears to be 10Ah. http://www.twfracing.com/PartsPages/shorai.html is a list of the available Shorais and prices. It appears that the ones with L2 use the smallest case, same as A2. I don't know which polarity will work better where you're mounting it. I'd go with LFX14, A2 or L2 based on wire orientation.