I now carry a 12 Volt LI battery to use if this happens again.
I carry one as well. It worked perfectly the first time I had a dead battery after leaving the car for 6 months without a battery maintainer. The second time, after being away from the car unexpectedly for 5 weeks, the fully charged jump pack would not power up the car.
That was near the 4 year mark, and having had a dead battery twice, I opted to go get a new one rather than try to revive the old one.