Batteries.

Hi All
Im sure I had this in one of my posts..Cant find it now.....
I had intended to use the orig reliant battery,or at least one of that small physical size,But now I find that it will be too tall by about an inch or so. Its a 32ah-390amps one.Havent looked for others yet ,but I reckon that there wont be one any smaller in casing size than that. What other types are out there that will do the job? I seem to remember gel cells being mentioned,but they needed frequent charging?
I intend to fit the battery suitably insulated , next to the petrol tank in a custom made cylinder that mounts transversely behind the pillion.This will allow a larger tank capacity .
Rod