Motorbike as a BOV, help please.

[Oimccoy]

most older bikes will run without a battery, all that does is run the lights and the horn, post SHTF you don't need any of them and its just another thing you can do without.

Only models which have self exciting ignition systems, a lot of late 70's and 80's Honda ran these ignition systems, a quick look at a wiring diagram will show you if it is such a system, anything with points will require a battery.

My suggestion for a bug out bike would be the old twin shock XL125 with a CG125 engine fitted. The engines a pretty much bolt in interchangeable, the whole vehicle is so simple you might as well buy a rolling frame and rebuild the forks, fit new bearing throughout and get the wheels re-spoked and re-rimmed - all of which wont break the bank. I'd prefer the twin shock version cos if your using a monoshock off road predominately it will shorten the working life of the bearings in the linkages and the shock by quite a lot, and post shit flying where are you going to get replacements from.
The cg engine tends to last a lot longer than the ohc cb especially when oil changes get neglected and all but the very earliest cg's run a self exciting ignition system.
While I would use all Japanese components due to their better quality if you do find yourself with a blown engine/CDI/coil etc all these components can be pilfered from a literally thousands of Chinese Honda clone 125's which zipping about.

OK, its not going to to give you huge performance but the light weight of a 125 is a massive bonus when (not if) you drop it if . and the lack of weight is always good