I've been struggling with my trail cameras for a while. The cameras would just shut down, miss days in a row of any shots, etc. I thought maybe it was my cameras, Moultries that are a few years old, but now I know it was the batteries. So, I got digging into batteries after this happened. I had been using the Eneloop pro rechargeables. Turns out, the output voltage for rechargeable batteries isn't good enough for reliable trail camera usage. I felt a little dumb for it taking so long to realize this. I had used Eneloops in so many other gadgets that I never thought they were the issue. I still love them, just not in my trail cameras.
I now run Energizer lithium batteries (not rechargeable) with good success (there is a good deal on 12 packs right now on Amazon where the cost comes to just over $1/battery). These batteries last for quite a long time so it isn't too big of a deal but it is still costly, even at $1 per battery. I did some poking around to see what alternatives there are and general consensus seems to be that the lithiums are the way to go. Alkaline batteries work too but only in the warmer months. They suffer in cold weather.
That's what I know and what I am currently doing. Anybody else doing anything different? Anyone doing any kind of jerryrigging, say, working up a harness to run 18650 type batteries instead of AA? I've done some googling and can't find much. I might just have to try this, I've got extra time these days!