A real smart battery charger (for AA trail cam batteries)?

Can't specifically recommend a charger, I've not tried your experiment with mine to see what it does - though you may find that reporting fully charged when it's not really is actually normal (depending on the battery type). However, most trailcams recommend you don't use rechargeable batteries in them - the voltage is a bit lower than normal batteries and they can cause poor performance. The best batteries are usually lithium - Energizer Ultimate Lithium are very good. They are expensive but last ages (many months in my Browning cam) and cope with the cold much better.
The other option, if you're using the camera in your garden, is to run a cable back to a power supply in the garage etc and run it from there. Or set up a small solar panel and 12v battery in a nearby shed perhaps.

I have tried many batteries and chargers for my headtorches and lights.
One of the best I have found is the Nitecore Intellicharger. It's worth looking at. The Nitecore batteries are pretty good as well.
There are several models, designed for 2, 4 and 8 batteries, the i2, i4 and i8.

Ah, good point.

I forgot to mention I would need one that charges 8 batteries at a time.

The memory effect (where the battery loses capacity if you only part-charge) only affects NiCd and (to a lesser extent) NiMH batteries - Lithium rechargables aren't affected (hence you don't need to flatten your phone every time nowadays). You can still get a temporary effect with NiMH but the full-drain should fix that (but you shouldn't need to do it every single charge). You can either get a charger with the draining facility or simply bung the batteries in a torch and leave it on (use one with a bulb, not LED, it'll drain quicker).
Panasonic Eneloop chargers have a drain feature I believe, so may be an idea to look at those - their batteries always seem to get top scores too, so they should know what they're doing with this stuff

As the others have said, its difficult to comment on the battery charger in question.

One thing I have noticed, is often metering is relative, and to what.....

The photographers among us will know what I mean when we see (often digital quotes) zoom magnifications as a 6x, 10x etc, rather than relative to the accepted 35mm camera optical zoom.

It might be indicating the batteries have dropped to 75%, but they may actually not have dropped that much in reality over the initial voltage. What you will get with all rechargeable batteries is what's called surface charge and sometimes this is measured as the main charge, which will be considerably above the nominal voltage, and will naturally deplete once the charge has been removed.

The best way to check whether a battery is fully charged or not, is using a voltmeter, and if the voltage after a period of time, around an hour or so, and definitely not when the battery is warm after a charge, is around the nominal voltage, then the battery is deemed to be fully charged.

This is the one I have.
It charges each battery individually, showing their respective charges.

www.nitecore.co.uk/.../nitecore-new-i4-intellicharger.html