Running one without a battery can result in some pretty healthy voltage spikes. The battery acts as a "shock absorber" in a charging system, so trying to run it on just the generator will probably end up with the electrical system seeing some pretty high, and very unpredictable output from the generator. If it hasn't been run in a while, it's also possible the generator will have to be polarized, and a battery in the system is definitely needed for that operation. The dry cell lantern battery is a possibility, but it won't last long, and the generator will not recharge it.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!