Hybrid vehicle has not been used for several months due to COVID-19 pandemic. Vehicle has a 3 year old 12V AGM battery. Battery is not used as a true "starter" battery; it just boots the vehicle's computers so the hybrid batteries can start the ICE.
Vehicle is not located near any electrical outlets.
The 12V battery was not cheap, and I would prefer to continue to use it for cost and environmental reasons. The battery might still be under warranty.
With all that in mind, which option is best to get the vehicle up and running again?
Buy a battery maintainer. Pull the battery from the vehicle and charge it for 1-3 days somewhere safe using the battery maintainer.
Buy a portable jump starter. Jump the battery to get the vehicle's computers running, and start the vehicle's ICE. Drive around for an hour or so.
Buy a new battery and recycle the current one.
Note that #2 is the easiest (no pulling a battery required) and that #3 is much more expensive than #1 or #2.