Smallest lithium battery to use safely with Victron Orion-Tr 12/12-9A

I want to use a small lithium battery to occasionally power my 2 dashcams when I’m out the car.
A battery small enough that my 20w solar panel can trickle charge it over long periods.
I was thinking even around 8ah would be ok.
What is the smallest ah battery I can safely use with the 9a victron?
Is this an ok setup?
An Orion-Tr 12/12-9A directly connected to a lithium battery and the victron output voltage set to the perfect charging volts for the battery?
Or do I need an orion smart dc to dc charger?
I just bought a dc to dc charger (not a victron), but it’s 40a and I was told I need at least an 80ah battery which my solar panel would not affect much and a large battery adds problems of finding space to fit etc.
The smallest dc to dc charger I can find is 20a but that needs a minimum of about a 30ah battery.

If you want to charge your battery from a solar panel, you need to use a solar charge controller.

Having used a 20w panel to power a 5w led light for 8 hours overnight (40Wh total use), a solar mppt charging a 20Ah LiFePo4 will not always keep the lights on.
Seasonal sun angle/shade and bad weather will eventually lead the battery to fully deplete

You better work out how many Wh your 2 dash cams will use per 24 hours. And design the charging system (panels/mppt) and how much storage (battery) you need.

I forgot to mention I have a dual battery solar panel controller to trickle charge my car battery and auxiliary battery.
I will only use the dashcams for short periods maybe 1 or 2 hours and only occasionally.
So the rest of the time my lithium battery will either be charged while I’m driving or while the car sits for days.