There should be a failsafe program that will allow the volt’s GAS engine to be jumpstarted when the 12v AGM is dead.
My 2017 went completely dead after 5 days parked at the airport. I could not get it going with an emergency jumper all it did was provide some power to the electrics but failed after the AGM sucked it dry. I could not get moving immediately as all our luggage was on the ground as the jumper was still attached in the luggage area etc.
I basically had to get another vehicle to charge up the AGM suffiently to safely get going.
Dead batteries happen and there should be a way to get that motor going while parked in an emergency.
If it is in the manual, sorry but I could not find it.
If the 12V AGM battery had developed an internal short in one of the 6 battery cells it could account for why the small LiPo jump starter could not jump start your Volt. If you had disconnected the battery cable from the negative terminal of the 12V AGM battery the LiPo jump starter would have been able to boot up the Volt's 12V systems. Once the Volt's system had been booted up the Volt's accessory power module (APM) provides power for the Volt's 12V systems, you could disconnect the LiPo jump starter and even leave the 12V AGM battery disconnected and the Volt would continue running. (Not sure why you could not keep your Volt running; once the Volt powers up the APM should keep the Volt running even without the LiPo jump starter connected and a dead 12V battery (a failed 12V AGM battery with a dead short in one of the cells would draw an excessive amount of power put a large load on the APM system.) If there is a problem with the Volt's APM system that might ultimately be the source of your 12V AGM issue.
There is another possibility. If by mistake you had started the Volt in maintenance mode (initiated by pressing and holding the Start button for 5 seconds) then the APM would not be activated and the Volt would only be running on the 12V AGM battery and/or the LiPo jump starter for as long as the 12V battery or jump starter charge lasted, then the Volt would shut down for lack of 12V power.
There is no conventional starter motor or alternator in the Volt. The APM takes the place of a conventional alternator and provides 12V power for the Volt's 12V systems and accessories when the Volt is powered on. When the Volt needs to spin up the gas engine, motor generator A (one of the Volt's two electric motor/generators) is coupled to the ICE via a clutch and planetary gears and spins up the gas engine. In this application MGA is functioning as a 100 HP electric motor powered by the Volt's 340V traction battery. MGA effortlessly spins up the Volt's gas engine.
If you want to start the Volt's ICE, open the hood and the gas engine will start provided the Volt has been powered on.