I only have a few days of 'testing' but I think a power pack will work fine. The 2 power packs shown below are rated as 10,000 mAh although the larger one is actually an auto/motorcycle jump start power pack. I've been using the smaller one for a few days and after a couple hours of dash cam use, it still shows fully charged.
I'm new to 'dash cams' so I picked up a 'cheapo' thru Walmart (iZeeker GD100) for 24 bucks! It's a basic forward cam but with impressive features if you can navigate the setup menu (had to download the full manual from their website). You do need to provide your own micro SD card. It includes a very long power cord but also a 12" one that works great when using the power pack, stashed in the upper shelf.