I am sure the topic of RPi power has been exhausted but I just discovered a new warning/something-to-gripe-about:
Recently I purchased a 12V battery power distribution panel from a reputable firm. The panel has the usual 12V fused PowerPole connector outputs. Also it has two 5V regulated USB-A outputs. How nice is that? Now I can power my two Raspberry Pi's. I tested the no-load voltage out of one of the ports and it was a cool 5.02V. Wow, I thought, they must be using one helluva good regulator. Well, it turned out that the stinking thing drops to 4.6V at 0.5A load. The Pi will actually complain about under-voltage when you hook up a monitor. I didn't do that. I ran it headless. After just a couple nights of imaging the VAP dropped out. I tried a proper PSU to no avail. I tired re-flashing the SD card -- nope.
I use one of these 12v to 5v regulators, connected to my Pegasus Ultimate power hub, works like a charm...
Stellarmate OS on Raspberry pi4b
Skywatcher EQ8 pro, on steel pier
Takahashi FSQ85 & Meade 8” SCT (de-forked)
Starlight Xpress SXVR H18, SXVR M25c, Lodestar x2 Guide Camera
Pegasus Ultimate Hub V2 for all USB & Power
Pegasus focus motors on both scopes
Highkamp, it wasn't me but it seems easy to do. You need a buck converter, like this one I use: www.adafruit.com/product/1385
and a 11.1V 5000mAh LIPO battery. Off the top of my head you should be able to get 2.5 hours out of a full charge assuming you draw down to 50% then stop, the Pi + USB devices draw 2A continuously, and the efficiency of the converter is 90%.
The challenge is what to do about the real energy hogs: dew heaters and TEC coolers. I use two 12V 35Ah deep-cycle batteries. They are light weight and won't break your back carrying around. I can go 6 hours powering a cooled camera, two Pi's, a RA stepper motor running continuously, dew heater, Flip Flat, Filter Wheel, and a 12V-to-19V boost converter to charge the laptop.