I bought this one a couple of years ago. I ended up not using it as planned because it wouldn't power my laptop. It claims to output 130w. I'm considering using it to power a heated bird bath and possibly an outside cam if I can figure out a less expensive way to keep it out of the elements.
if you're just looking for it to fit in your pocket, i have a zendure brand one that is barely bigger than a credit card in its dimensions, but its 10k mah, 45W. It's about an inch tall. I know it's not 5,000 like you are asking, but might fit the bill size wise
You can get water proof electric junction boxes at your local big box hardware store for a few bucks. Get one with only one port and use a cable gland to seal the cable. You can also get waterproof connector pigtails so you can remove the battery without messing with the case.