I recently acquired a dashcam, and I am looking at plugging in the USB end to a portable USB power bank. Are there "types" of batteries that are better for extreme temperatures, or can I really just go with any (decently-rated) product out there?
A regular LiIon or LiPo powerbank is not likely to be a problem if you're not in the hottest parts of the US. You just want to be sure it's never left exposed to direct sunlight.
The key to LiIon safety is using only quality cells and never exceeding the temp range when charging.
Why not do what I have done? A 99A LiFePo4 battery under the seat primarily to power my fridge and air heater. I have fitted a cigarette lighter plug and connect the fridge and dashcam to this.
My dashcam is on 24/7 and just my short 15 minute drives to work keeps my battery at 100%. An advantage is that the power it recieves is the power you have, unlike wet batteries where you have to wait 24 hours to see the actual charge the battery has taken in. The high readings you see on the wet battery just after a drive is surface charge.