1969 Triumph T100 Battery Size

Hello Folks,

I'm trying to find a compact battery which would fit the 1969 Triumph T100 Daytona. As it's a cafe racer, space is a bit restricted, so I was wondering if a) it's possible to run it without a battery using a zener or similar and will it start easily without one, or b) what's the smallest battery size I could use at a reasonable (ie. minimal!) cost?

Cheers, Mike