I have one of these little car jumper packs. Basically, it's a small #lithium #battery you can attach jumper cables to, but it also has an LED to work as a flashlight, and a couple USB ports for power. You charge it either from a wall cube power supply, or a cigarette lighter plug. It's rated for about 60 watt hours of capacity. The brand is Powerall, but there are similar products under different brands/manufacturers.

I wanted to see if I could use it for powering bigger things, eg amateur #radio gear. The alligator clips have a weird blue connector on them, which plugs into the end of the jumper pack. It turns out this is an #EC5 connector, which is actually used more with lithium batteries for things like radio controlled vehicles. I found some online, and made a pigtail adapting them to Anderson #PowerPoles, with a fuse inline. I haven't tried powering anything huge, but it works.

If you attempt this, keep in mind that I'm not sure if the jumper cable connector is switched, or if it connects right to the battery (I suspect the later, I haven't opened it up to check.). I'm not sure how aware the BMS is off power out that port, so you'll want to keep an eye on the voltage. It may let you drain it completely, which probably isn't good. That said, since it's meant to be connected to a car starting battery while you try to crank the engine, I assume it can take something of a beating. A fuse is a good idea too.