I made a battery powered mobile portable Wyze camera with a small 12V AGM lead acid battery and a little USB power module. The battery is a Powersonic PS-1270F1, $20 on Amazon. The USB power converter takes 9-24V input and converts to up to 3A, 5V USB output. About $1 or less on Ebay. And a $0.10 on/off switch.
I measured ~300mA normal daytime operating current @5V on the Wyze cam, and ~380mA at night with the IR LEDs turned on. I easily got 24 hours of operation on it and the lead acid battery was 12.3V at the end of 24 hours. I am going to test it again and let the battery drop to 11V and see how long it lasts.
On the next phase of this project I will make a battery voltage detector that automatically shuts off the power when the battery reaches 11V. You don’t want to drain lead acid batteries down too low, that will reduce the life and capacity of the battery. I charge the battery with a lead-acid battery charger.
(I have more pics to upload but I am only allowed to post 1 pic since I am a new poster.)
NIce! 
My setup isn’t mobile, but similar to yours… I have attic cams on their own account and network attached to leftover stuff from my motorcycles and a 5 year old Group 27 deep cycle marine battery. Battery is constantly on a Battery Tender Plus, all cams connected to the marine battery via Battery Tender 12v-USB adapters on 25’ power leads. I’ve gone 8 days without charging power with cams set to continuous recording to SD and NV IR lights on. Not sure what was left in the battery before I noticed that my roofing contractor left my tender unplugged, but it works great considering I used leftover project parts to rig the whole thing.
Hey guys I’m thinking of a similar project, did you determine the ultimate run time without charging?
I started to think about how to make a simple low-power cutoff switch, and I was kind of stumped, and never got back to it.
I have only used it a few times but I didn’t let the battery go much lower than 12V.
Ok I’ll turn it on right now and run it to 0% battery. I’m going to define 11V as 0% battery. I’ll report back in a couple days.
Configuration: With SD card but only recording motion. IR night-vision LEDs off.
Not 100% sure if it is what you’re looking for, but some of these fuse kits have battery protectors that seem like they could work. They’re used to keep the battery from dropping so low that the car wouldn’t start.
That is a really cool product, I might have to buy that for my car dash cam. But it says it cuts off automatically between 11.6-12V but I want to cut off no higher than 11V.
Test finished. The battery lasted 65 hours and I let it run down to 11V.
It lasted longer than I expected.