Street legal requirements vary dramatically from state to state. When the OP finds out what state he lives in, an informed person may be able to tell him if a battery is required to get a plate in that state.
I believe in CA, the battery requirement is so that the tail light can remain lit for an extended period with the motor off (I thought 20 mintues, but can't remember the exact figure).
For the dual sport bikes I've done in California, the state required a certified lighting inspection station to sign off that lights worked. On mine, the certified lighting inspection station (a motorcycle repair shop) always checked for the battery, and for tail light operation with the motor off. Other states will differ.