My 2013 Prius Plug-in seems to be vulnerable to battery drain when sitting idle for too many weeks. We have had it checked out, have met with very competent Toyota technical team members, and the conclusion is that if the car sits idle for too many weeks, the small 12-volt battery will drain and the car will require a jump start. This seems to be an inherent problem, not widely known or discussed. Though the car may be switched off, there is a small (50 mil amp, I am told) drain on the 12-volt battery, in order to power the computer systems of both the basic car and the plug-in module. If that battery drains too low, the car will not start. I am told that a certain level of charge is needed to power relays and computers. It is also critical that the key be removed from the car or additional drain will happen. Obviously, all lights and systems must be turned off. This situation is clearly a problem for people who do not drive every day, who may be out of town for extended periods, who may have bought the car for second-home usage where it might be idle for long periods. We have had problems when the car sat idle for just 13 days. We live in New York City and just don't use a car every day. We park in a garage within our building with trusted attendants. However, a friend in LA who has exactly the same model and year, has survived dormant periods of 3-4 weeks. The dealership and the regional Toyota technical staff could not have been nicer nor more attentive to our problem. They thoroughly checked out the car and even replaced the 12-volt battery, though it showed no problems. This just seems to be a fundamental problem of this model, one that seems to have no solution, except for committed usage of the car. Do we mark the calendar and go drive the car around just to charge the battery? Environmentally incorrect and massively irritating, but necessary? The Toyota team did suggest a trickle charger be attached to the car to mitigate the problem and keep the 12-volt battery up to proper charge. This is a little tricky for us within our garage, but we will try it and see. I believe that Toyota should be more forthcoming and transparent about this problem, so that unwitting buyers/lessors do not commit to a car that doesn't match up with their lifestyle. I am not pleased at the discovery of this basic flaw in the car with about 2.5 years remaining on the lease.