Last year I was able to do 12 days with over 250 pictures on one battery. I think it depends a lot on exactly what camera you have. With my old camera I had to take a spare battery. But the camera battery is really light weight - it just is expensive to get a second one. You might consider getting a new camera.

I also am very careful not to do anything but take photos - no looking at them at night! I also sleep with my camera if I want early morning photos. I have found that when apparantely "dead" the camera does fine once I warm it up. My camera has a metal case and quickly gets cold.

I do not take extra batteries on a backpack. I do not use a GPS, I hardly ever use my head lamp, do not take a cell phone. I probably would not take these items even if someone came up with a light-weight solar charger.

I use passive solar energy as I can - pre-heat my water bottles before cooking and washing, melt snow, set up camp in a location to get early morning light to dry the tent. I do not go out in the wilderness to replicate civilization.