Simple electronics circuit to keep power bank alive?

[Oldman]

Have you seen what fox cubs do to any wire at there level I used to have multiple Sat dishes up to 2mtr in my large garden. All the cables were run in 4 inch pipe but where they rise out to remote control the dish's I had to chicken wire them or the fox cubs ate them!
I have a few gel type 12v batteries that I use for echo sounder/fishfinder etc and I do have some 12v to double 5v USB socket converters so I can go that way but its just for me so much simpler to attach a power bank.
My trail cameras work quite happily off 5v dc, they just report 70% battery as its down from 6v its expecting.
No hogs last night, but I did have 2 Magpies in daylight shouting at a fox while he ate his pasta, they were just 3ft away. They bullied him off the food and repeatedly took mouthfuls back to their nest.

 

[Oldman]

I bought a couple of USB male & female flying cable ends with split covers from ebay cheap cheap.

I had some suitable 1 core and sleeved screen cable and some resistors so I made up a flexible lead with 200 ohms across as a load. That works fine with my current 5000mAh power banks as a keep alive.
I also found https://www.sotabeams.co.uk/usb-battery-pack-keep-alive-load/ who do an inexpensive kit or pre built to enable you to keep any power bank alive as it has adjustable load via a trim potentiometer.

I bought a kit, took 30mins with a fine soldering iron and my best reading glasses to assemble and test.
I checked the minimum current needed to "keep alive" 4 different size power banks that I have and the results were:

5000mAh pack (10seconds to off) 20mA load to keep alive

20000mAh pack (30 seconds to off) 40mA load to keep alive

30000mAh pack (20 seconds to off) 75mA load to keep alive

32000mAh pack (20 seconds to off) 50mA load to keep alive

So its easy now to find what load it takes to keep a pack alive, I quite fancy one of the 555 timer kits to save more battery power but its just boys toys, I can do what I need with the little 5000mAh packs for now