Someone can correct me if I'm wrong, but my understanding is the 12v battery is charged from the main battery using the DC-DC convertor, which is only active when a contactor is closed that happens when you key the bike on. It shouldn't really take too long to top it back up. I'm not sure how easy it is but you could always just disconnect the 12v battery if you can do without the always on cell connection.
The following is my experience with a 2020 SR/S. I charge to 75% and then ride or let the bike sit in a garage. When the bike discharges into the 40's, I recharge. I still have the ZeroNG app, which I think is now banned, so I can monitor my 12V battery daily. The 12V SOC fluctuates from low 12's to 13 something. So, with no key in the bike, the bike takes care of the 12V battery, both the charge state and by running current in the 12V battery heater. Also, the bike will go into storage mode if I don't charge or key on frequently enough.
I'll also add that to check the 12V SOC with a meter, the terminals must be disconnected. The battery heater has a separate connection to the bike, which has to be separated if removing the 12V battery.
If monitoring the bike remotely, note that the State of Charge displayed won't be current if the bike has powered down the cellular connection. ZeroNG shows the date of the last update.