Oh, I was going to mention that, but I forgot! The image was stacked using StarStaX. I don’t know much about it, as I’m just learning to use it myself, but in my opinion, it does a very good job! It’s quite fast too!
As for battery shut down issues, I think any of the more modern cameras will save your exposure before they shut down. I’m quite certain that my Rebel T3 will. I would suspect that the older cameras like the 40D and so on may not, but I have no way of testing that!
I have not really had any long-exposure battery problems. I can take several hours worth of exposures with my Rebel T3 without draining the battery. According to snapsort.com, the Rebel T3 has nearly the longest battery life of any entry level DSLR, and I would certainly believe it!
A note on battery life: Just before I left for Africa, I purchased a new batter for my T3 as I had no idea if we would be able to charge them while we were there. That brought me to a total of 3 batteries, the OEM Canon one that came with it, a Chinese no-brand one from Ebay, and the last one, a slightly more expensive Opteka brand from Amazon.com. I figured that since it’s been almost 2 years since I got my camera, the batteries were probably starting to wear out. During the first 3 weeks, I hardly used my camera, although I did do a few star shots, but nothing more than 5 minutes. As far as I can remember, the battery lasted till we started traveling through the Etosha Game Park, where I took several hundred pictures. All of a sudden, the battery was dead. Oh well, I have two more “freshly charged” batteries! The next battery lasted for no more than 200 frames when it too was dead! Now I was starting to worry, I only had one “fresh” battery which had been charged 3 weeks ago the night that we left for Africa. I started trying to cut down on battery use as much as possible, I turned off the Image Stabilization for the lens, limited the time spent viewing pictures, and turned it off whenever possible. By the time we left the park, that battery too, was blinking red. I started to suspect my new lens as the cause of the sudden battery drain. Come to think of it, I never noticed that my batteries were starting to “deteriorate” till I got the new lens. I can often hear “clicking” and see the viewfinder jump, especially when turning the camera on/off.
We stayed in South Africa for a few weeks afterwards which was where I took the pictures posted above. During that time, I took several long exposures, and the battery held up just fine.
So, learn a lesson: I strongly considered buying a 12V DC battery charger (for use in a vehicle) along with my new camera battery, but it cost all of ~$25 dollars, and I finally decided against it. I wish now that I had! What is $25 compared to pictures from a country that you might never visit again!