I'm pretty sure that would mess the battery up if it's a normal battery. I'm sure that someone with more knowledge will chime in shortly.
Try the sycle batteries. the 4.6 one should cover everything needed and tiny. Expensive, but no need for trickle charge and last 5 or 6 years. I know Bandino has one on his build and he said he's had no problems so far. I'm going with this as soon as I get to that point.
http://www.testsycl.com/Home_Page.html
http://cx500forum.com/index.php?/topic/6583-pics-of-build/page__p__75075__fromsearch__1#entry75075
This would do you.
http://cgi.ebay.com/GEL-ATV-MOTORCY...772456205?pt=US_Batteries&hash=item3f0b4bcb0d
Cheap brand so probably not top notch but then learn to bump the bike off(Advantage of having a CDI ignition bike<grin>![]()
It does have 14 amp hour but may not work with the Starter well(Service Stater motor if you haven't yet anyway).