We started with the 1 battery that came with the lightweight trailer seven years ago. We were given a brand new battery two months later and thought we were in heaven. We read at night with headlamps and that was great. We eventually changed to LEDs, as a number of respondents have suggested. Doubt if you need more power for three day weekends.
Might use the outdoor shower so that you don't fill up grey water. Ours has both hot and cold faucets. Would suggest getting a propane heater such as the Olympian Wave. It keeps the cabin warm at anything above freezing. It takes no electricity and all the heat remains in the cabin. The burn products are water and carbon dioxide. You should leave 3 square inches of window open to replenish oxygen. The forced air heaters blow about half the heat to the outside and are real energy hogs. We generally boondock and almost never stay at RV parks, but you can hear the generators going on at 3 in the morning because their batteries are dead and the heaters are not working.
We did go to solar and it is a slippery slope "the more you have, the more you want!" We cannot imagine traveling without it. Something to consider in the future but not needed for short trips.
Reed and Elaine