You need to keep a trickle charger on your battery while it's not being used. The chassis battery voltage can low enough in a month, due to parasitic draw, to disable vehicle start. Things like the radio, transmission, and various computer modules have a constant draw on the battery.
I've been using a charger called Battery Tender Junior for 10 years and haven't had any chassis battery problems since. I started using one after I figured out there was quite a parasitic draw from various devices. I also replaced a battery before I figured it out.
2015 Greyhawk 29MV
Honda CRV toad with Blue Ox baseplate
Ready Brute Elite towbar with braking system
TST 507 Flowthru TPMS