Bill,
I'm not sure what you mean by 'size'. I have enclosed a link showing most automotive batteries (not Optima) by group number, which is the physical size of the battery itself.
The 'electrical' size would be its CCA (among others), or cold cranking amps, which would give you a clue to its oink and sustainability.
If you are limited on physical space, you might be limited on battery selection too.
http://www.rtpnet.org/~teaa/bcigroup.html
Stuart
