Ran out of room, need a smaller battery

So I built the whole back half of my kz750, custom swing arm and seat and all. But I ran out of room to put things, so I can no longer fit a regular sized battery without making big changes. I wanna put a small lithium 6 or 8 cell battery just under the seat. Does anyone recomend this and if so do I need a different voltage regulator to run it?

I'm sure there are naysayers here but my personal experience with lithium batteries has been great. Excellent cranking power and very light. Earth X has a two year warranty on their batteries, I'm not aware of a lead acid battery manufacturer offering a warranty even close to this. I upgraded my regulator to a modern unit as lithium batteries don't like a wide swing of voltage for charging. I have not had a problem except when I had a parasitic draw that drained the battery completely down to 1V. Lithium batteries usually are junked after you do this, however I was able to charge mine back up and used it for a year before it crapped out completely

What kind of regulator did you use? Thank you for your time sir.

ricks motorsports standard regulator, but i see they offer a lithium specific regulator now.