You're overthinking this...
Just grab a 6V lantern battery from Wally World.
If you're worried about letting the magic smoke out, use an inline fuse.
1983 Suzuki GS850G, Cosmic Blue
2002 Suzuki Vstrom DL1000, Midnight Blue
2005 Kawasaki KLR650 - Turd II, The ReTurdening
"Do not crinkle your food wrappers loudly. Be considerate to others, or I will bite your torso and give you a disease."