I can answer the generator question, at least for 2-ft locomotives used at the WW&F Railway Museum. Our generator, made by Pyle-National a prominent maker of such things, is rated at 350 Watts. Since the headlight is 250 Watts, that leaves 100 Watts total for the pressure gauge light and water gauge light (and cab light if we had one). The headlight and rear light are controlled by a double-throw switch such that they cannot accidently both be on at the same time. The voltage used is 32 Volts DC. Now (finally) the answer to your question: there is no battery.