Power issues!

Have you check if the 8-40V regulator can regulate enough Amps?

The power circuit on that battery can't supply the necessary current to support the voltage when you use it to power the cooler on board these cameras.   If you must use a battery source simply get a larger one. 

While that battery should be able to handle the load it is not doing it.  Perhaps there's a cell inside going bad or something faulty with its internal DC to DC conversion circuit.

I would try a new battery, and even something larger actually to handle camera cooling and tracking mount for hours at a time.

edit: I looked at the web page for the battery and I don't see a continuous rating on the 12v outlet, just a maximum rating.   The only amp ratings are for the USB level outputs.  I think you are simply overloading for that application.    153 watt-hours for the battery is on the small side for imaging with a running cooler unless you are keeping it to just a couple hours at a time.

I have been using the same voltage regulator for a a long time without issue. However I’m using a much larger battery. The low voltage can be the result of a poor battery pack as mentioned before, volt drop on you supply cable/connectors or possibly both.  If the issue is the battery pack then the voltage regulator won’t help, as the issue is power not voltage. However, if the issue is volt drop then you could help matters by using a cable with a larger cross sectional area. I’m using a pair of 10AWG ultra flexible Silicone wires to feed my switch from my battery. And ensuring that your connectors are of good quality with low contact resistance. 

Update!

It was, indeed, the wiring. I was using a DC splitter near my power supply that was only rated for 5A.
Whilst my setup only consumed about 3A, it was enough for the thin wiring to cause a voltage drop. I've replaced the splitter and am now sitting at a comfortable 11.4V 

Thanks guys!