You mentioned medical device, that's what started this. Mrs.tiller spent a week or so in the hospital a while back and when her tablet ran out of juice, I brought in a 6' long 14 gauge power cord so she could charge it up.
The nurse suggested I take it back to my truck before someone from engineering sees it and confiscates it. They consider anything of mine plugged into their outlet is a fire hazard.
Just imagine how to use some of the suggestions here - Car battery, tractor - heck just carry a 10K generator around.
How big are your pockets and wallet?
I've usually BIG pockets and a small amount of money to spend.
I've about dozen Li-based battery banks of various size, from the Anker size that Darryle posted to a
GOOLOO 4000A that is rated to start my tractors. All fit in my cargo pant pockets.
My uses are primarily:
- running Wyze cameras and a wireless hotspot
- Starting my wife's 1994 Honda Civic (I use a
HF Li-Fe)
- Providing power for cellphones when my wife "whoops, forgot to charge the phone".
All of them seem to keep a charge for years. Generally the bigger you go the more power you can store. Many
include LED for use as a flashlight. The larger ones have multiple outlets for various uses.
For the Wyze case I'm partial to the little
Samsung 10Ah, mainly because they kept going on sale for $13@. It will run a camera recording to SD card for about 2 to 3 days. I pop the battery in a ziploc,) place the camera. If I need my Mobley (wireless hotspot) I can plug that in also.
For my wife's Civic I've the HF Li-Fe which will start it several times. Holds a charge for years.
And for the "whoops" I have her carry one of the Samsung or one of the little Anker sized ones.
From what the OP posted about his uses I'd recommend a couple of the 10Ah size when they go on sale.
The GOOLOO is nice if I have to crank my tractor but heavy to carry around JUST to charge a cell phone.
Besides size and price also consider danger. LiIon explodes:
The HF charger is LiFe, not very explosive.