why do you need to have batteries in the camera with an aux setup?
You need the rechargeable battery to "store" the trickle charge from the solar panel. Basically, the panel tops off the battery during the daytime sun, then the battery powers your camera while it takes pictures all night long. And you DO need rechargeable batteries, not alkaline or carbon-manganese.
If you live on or near your lease and can change out batteries weekly, I probably wouldn't bother with a solar hookup. If your lease is too far to go weekly, I would definately go solar.
BTW, you don't need to buy a charging unit from the camera manufacturer, but I would if your camera already has a port for same. If your camera isn't set up for a charger, you can drill a small hole in the bottom of the unit and run a wire with aligator clips inside and clip on to the battery lugs. But be aware that such a modification would likely nullify any warranty on the camera.