Dead batteries and jumping these newer machines can cause a multitude of problems as voltage spikes kill ecms, circuit board components across a wide range of devices. Rule-1 is to never store something long periods without either removing the battery and keeping it on a maintainer or on one in the vehicle. Jumping a dead battery is not recommended these days at all. Start with load testing the battery and replacing if necessary...and it likely is. Next look for any rodent damage and anything else to narrow it down. You mentioned the garage is high humidity so also start looking for corroded connectors.
I currently have maintainers on all my things with batteries including my camper, daily driver if it is going to sit more then 4 days, two on my truck as it has two batteries, my handicap van, my 4500w generator I use for camping, and of course my ZForce 800.