smalles battery

i'm gonna make a tray for the electrics and battery for my 77 650 custom. the bike has martek electronic igniton. i am going to use the kickstart, so cca shouldn't be a problem, but the amp hours is what i am concerned with. thoughts?

I'd ask the manufacteres about their recommendations:

Motorcycle Batteries
www.yuasabatteries.com/ (Wet Cell Battery)
Dry Cell Motorcycle Batteries
en.wikipedia.org/wiki/Lithium_iron_phosphate_battery (Information)
www.batterystuff.com/batteries/motorcycle/kawasaki/
www.pegasusautoracing.com/group.asp?GroupID=BALLISTICEVO2
www.ballisticparts.com/products/batteries/12cell.html
www.spencercycle.com/category-s/232.htm
www.shoraipower.com/t-faq.aspx (information)
www.shoraipower.com

If the charging system is in good order, you can use a tiny battery from a Honda Spree 50cc scooter without any prblems. Just make sure it doesn't charge higher than about 14.3v. Your 77 charge system is adjustable (albeit crude).

The 77 system, when working properly, has plenty of excess capacity. Your Martek ignition should not use any large amount of power over a stock ignition.

If the Martek fails, you should be able to swap in a Dyna S pretty easily.