Nighthawk M1 MR1100 as IoT modem for vacant home

I set up my new Netgear Nighthawk M1- model MR1100 with a Simbase SIM card and it seems to work flawlessly with AT&T (set for roaming data). I am using the device as a modem for a vacant home to manage smart devices and security video. Since setting it up yesterday afternoon it has not ended a session as I have not seen any data billing appear on my SImbase account dashboard. Does anyone know how long before AT&T will force an end to the session? Is it 24 hours, 3 days, a week maybe?

I expect my Nighthawk will then automatically reconnect to the network but I suppose I should monitor that.

Second question- Can I remove the battery and leave it plugged in with the AC adapter and power cable? Or is it safe to leave the battery in and connected to the charger in case of a power failure? Because I don't think the hotspot will automatically restart.

Thank you.