I had to leave my 2015 Prius C sitting in my garage for seven weeks without starting it. It has 25,000 miles on it. Wouldn't start when I tried to start it. Had it jumped and I drove for about 20 minutes before shutting off. It wouldn't start again so I jumped it again. Drove for another 20 minutes before shutting off. Still won't start. The dealership I bought it from new, two years ago, is never helpful. I want to be prepared when I tell them what's wrong, and what they say needs to be done to fix the problem. I purchased the five year extended warranty. Thanks.
The car is constantly imposing a slight load on the battery. If the car is used regularly, it'll be ok. But: two years, old, sitting idle for seven weeks, it's been drained. Jumpstarting and driving for 20 minutes does not restore a dead battery. Depending on how motivated you are: 1. Purchase a smart charger, in the 3~4 amp range, one that's capable of assessing the battery state and running a charging session. Hooking up at the under-the-hood jump point is fine. It'll likely take around 12 hours to complete. 2. Head for your dealership, they can try similar, or more likely: will sell you a new battery. If you're going to leave the car sitting for 7 weeks, a smart charger can be left on, indefinitely. This'll prevent mishaps like this. A good quality charger would be the CTEK 3300.
Just as another data point, I left my 2012 Prius C with its original battery sitting in my garage in moderate temperatures while I went on a 7-week vacation last fall. On my return the car started immediately despite the neglected four-year-old battery, and it continues to work perfectly.
