Unfortunately, there are quite a few "parasitic" loads draining the 12V side of the hybrid battery constantly - the onboard cell modem (active even if you don't subscribe to a Kia Connect paid account), the proximity sensors, etc. And note that there isn't a specific 12V battery in this design. Part of the hybrid battery is "reserved" storage for the 12V side and is just converted down to 12V as needed. This is why they shut it down so quickly and offer the boost button to get it started again, as it could drain down the hybrid battery and make the car non-operational. However, I believe you can still jump it to get it started and charging again via the "+" post in the engine bay near the fuse box on the right side.
You can certainly take it to the dealer to have them test your hybrid battery and check for unusual parasitic loads. Otherwise, the only other option is to disconnect the 12V system via the connector in the engine bay when you go on vaca, but I believe that will also clear out your profile/radio/seat settings, etc. But if the car as been working "normally" before that and you have been getting decent gas mileage, its probably not a hybrid battery issue.
12 days isn't that long, so wondering if the 12V side got drained a bit via accessory mode, or doors open/lights on for a while while the engine was off just before your trip? Could just be a fluke. Hope it doesn't happen again!
