Moultrie A-8 Manuals & User Guides. User Manuals, Guides and Specifications for your Moultrie A-8 Digital Camera. Database contains 1 Moultrie A-8 Manuals (available for free online viewing or downloading in PDF): Instructions manual.

I have the same camera and have had the same problems. That manual is terrible and confusing and is missing critical info like basic specifications, including the 12V power jack.
I had to figure it out myself.
The qty (12) AA batteries (@1.5V each) = 18V. I actually measured 19.5V with a fresh set of batteries, using a multimeter on each of the springs of the battery tray.
So basically, the camera can handle between 12-20V. With AA batteries installed, it will select from the higher voltage source.
So if you have say, 13.2V in the aux jack and a fresh set of AA batteries installed, it will latch to the AA batteries until the voltage is the same/less than the aux jack.
I've been connected to a remote 12V battery for 8 months now and it's been showing 100% battery life, so that's the best way to go.

Moultrie Game Camera Manuals Downloads

The camera can get a little glitchy if the input voltage fluctuates substantially, like if you have 12.7V on the battery and then start to charge it up to 14V. The camera may snap some additional photos and/or miss a time lapse check in.

Moultrie Game Camera Set Up Instructions

If I can help with more questions please let me know, as I had to figure this out myself too.