Using the Prime while Camping

Power Bank, to me, is one of those "don't leave home without it" items.
I like to keep PBs in these pouches and cut little hole between two main inside sections to run short charging cable to phone. Normally these pouches go for about $5 free shipping.
Army Tactical Holster Military Molle Waist Belt Bag Wallet Cell Phone Pouch Case | eBay
I like this style of headlamps with Power Bank usb output feature. They use standard 18650 batteries so its easy to have lots of backup.90000lm 3XXM-L2 LED Headlamp USB Headlight Flashlight Head Torch Lamp Power Bank 707427700185 | eBay

When I get around to running Trailer Light wiring from trunk to engine bay I'm going to pull a few extra wires so I can run decent 12v from engine batt to rear (with enough extra to nearly reach front seats) to power stuff like laptops for mobile office. But I'm sorta wondering if that will be OK, or should I put another small car battery between the car's 12v batt and the laptop?