Best way to charge a LiFePo4 external battery from small solar generator?

[probablynotbill]

I've been looking at the Jackery 300 primarily because of it's small form factor and bi-directional USBc PD 60w port. My most frequent use case will be just to charge my laptop and allow me to work more outside and weekender car camping trips. Could I also use that bi-directional USBc port to charge and accept charge from a secondary external 50ah or 100ah LiFePo4 battery for extended use cases?

This is an attractive use case to be able to use the tiny ultra-portable form factor of the Jackery 300 with it's 100W solar panel most of the time, but be able to connect a better battery when I need the extra storage. In all cases the 300w throughput is adequate for my needs.

Would that work? What kind of cable / charger would I need to build/purchase to charge say an SOK 100ah battery and later draw power back to the jackery using the same system?

Thanks in advance for guidance!

 

[probablynotbill]

Would it work just to buy one of these https://www.renogy.com/12v-dc-to-dc-on-board-battery-charger/ (Renogy DC to DC charger) and just swap the direction depending on whether I want to charge or discharge the external battery?

Charing external battery: Jackery cigarette lighter port => Renogy dc to dc => LiFePo4 battery
Drawing from external battery: LiFePo4 battery => Renogy dc to dc => Jackery DC input barrel plug
(obviously I can't do this at the same time)

I could just wire up some little adapters to make it easy to swap between modes?