I have 2 18ah for my optical optimizer transceiver and receiver, and a 10, and 15 ah for the streamer. (See my system by clicking on my profile.) I use the LIFEPO4 battery calculator, it will help you determine the goals you’re looking for size and time: https://micropowergrids.com.au/Calculators/1_LiFePo4_Battery_Calculator.html
I wouldn’t want my 4 amp charger going into my delicate electronics, so I always charge detached. Oh I have 3 LIFEPO4 4 amp chargers for each of my 3 battery demanding parts of my HiFi rig. I cannot emphasize enough trying your streamer on a Lifepo4 battery, it’s truly remarkable. After hearing the clarity and transparency you can’t go back to AC. I really enjoy the ritual of new batteries for each listening session as well, feels like an offering to the Music God. :)
Link to my preferred chargers