I used to deploy, once, twice, yearly-for many years-I resolved this problem and never had this problem again.
While in Storage, I disconnected the Battery Terminals ( in my Trunk )
I purchased and installed a Solar Panel Battery Trickle Charger. something like $40. I hooked it up to the Battery Terminals and put the Solar Panel on the outside, trunk and secured it so it would not blow away, scratch my car.
6 months later, it turned on the first key turn!
Oh Yes, I also installed Stabil Fuel Stabilizer 2 days before, I ran my errands around town, so the Stabil was introduced all throughout the system. I put a Car Cover on it. ( Again, solar panel on the outside, laying on the car cover). I hope this helps! It did for me.
The battery is new, I had it checked for unusual battery drain and nothing was found but if the car sits for about 2 weeks, the battery is dead. It's in storage so I can not plug in a trickle charger. Any thoughts by anyone on what I can do to keep the battery charged at least enough to start it.