Portable 12 Volt Power Supply

[Oka]

Sometimes I need a 12V DC power supply. When no fully charged car battery is laying around, I would have to charge one up.
I just searched and found some. One thing, I would not want to spend too much on one. What portable power unit would one recommend?
Thanks.

[Pennhaven]

I keep a UPS replacement battery on hand for sundry portable 12V needs. (e.g., Handy to keep all the vehicle electronic modules powered up when swapping car batteries). There are a range of capacities available (https://www.amazon.com/s?k=ups+replacement+battery), depending on what your power requirements are. You can fashion leads with the correct connectors for the batteries terminals and with alligator clips, or any other termination you need, on the other ends. They are designed for deep discharge, hold a charge for a long while and are rechargeable with an automotive battery charger.

[Allgonquin]

https://www.youtube.com/watch?v=JN8A2nIMUWA

Here is a recent test of jump packs.