Appreciate the insight and back ground but would affirm the Why's . . . The Why's are dictated by how the entire system is integrated and tied together to achieve the final goal. Case in point your initial goal was to power the system via solar / wind.
The so called 12 volt solar panels are not / do not output 12 volts but 24~32 VDC. So a charge controller would need to be included no matter what. Which as you know depending upon distance requires larger diameter wire to reduce voltage drop.
Larger wire costs more, takes up more room, is heavy, and carries more current nor safe. As soon as you move away from the so called
Hobby solar you immediately go to 60 / 72 cells or more. These solar panels output depending on design, number of cells, result in 39 ~ 50+ VDC.
As is with the 12 volts system a charge controller must be used but the huge difference is again in wire smaller diameter, longer distances, lower current, and overall costs. As noted early on unless you wire a 12 VDC battery pack in parallel to offer longer ampacity (AH) you will always be in the danger zone of drop out.
The only saving grace is the vast majority of cameras have a wide operating range. Typically that's 25% of swing either way which translates to 9~15 VDC. So in theory a camera will operate fine in either extreme as it was designed to do so but what's the problem???
You can not, shall not, ever run a 12 VDC battery system below 12.3 VDC!
Depending upon many factors which I am sure you're aware of generally speaking a 12 VDC battery is considered fully (Lets ignore cell type, technology, chemistry, temperature for now). 12.8 ~ 12.9 VDC is considered 100% full. Unlike everything else in the world batteries do not reflect in a linear fashion of 100 ~ 0% as many falsely believe.
Anything below 12.0 VDC is a discharged battery . . .
I am being very specific when I use the phrase discharged vs flat / dead. Anyone who believes otherwise doesn't understand basic battery theory or the *Why's. If you see a battery that is 9 VDC its garbage, you see a battery that is 11 VDC its garbage.
Every time a battery is allowed to fully discharge this I'm sure you know directly impact the number of cycles. So if it was designed to be cycled 100 times from full to (DOD) not flat! That is a cycle until the battery will longer hold a charge or provide enough power / energy per the 20 aH rating / 20~25'C.
As noted, to offset this issue people either use higher ampacity cells or parallel them to do the same. This again doesn't address the fact you do not want to run a camera system in the lower voltage range.
Why???
Because unlike pure resistive (Ohms Law) voltage and current does not follow lock and step. It actually goes up (current) while the voltage goes down.
Why???
Because that thing called a regulator inside of every 1st / 2nd tier camera is what enables it to operate in those wide voltage ranges without dying . . .
So if its still able to operate at 9 VDC how does that impact a battery pack which is clearly not discharged vs flat / dead??? And literally every time you allow a battery to go flat / dead reduces its cycle life by 30%! Meaning if said battery pack had 100 cycles and all you did was run it flat / dead you will have 70 cycles left!
Obviously this depending upon the type of chemistry / technology in use but the basics never change. Because if it wasn't true there would be batteries in every type still running now . . .
NOTE: To be clear running a 12 VDC battery pack is fine its done everyday all over the world with great success. The difference is these systems were designed with a very wide margin of operations: Large ampacity per cell, paralleled, higher quality, never running below 50% DOD even if the cells are designed to consume up to 80% etc. Lastly, realistic run time and dedicated voltage cut off circuit (BCM) voltage protection circuit to protect against going below 12.3 VDC.