The 4-month old auxiliary battery in my 2012 Prius C seems drained randomly. Once in a while it becomes hard to start the car after parking for several hours. The battery voltage is low, only around 10.5V when measured in the fuse box under the hood on the passenger side. Most of time, however, it is fine. The voltage is around 12.6V. The car is always parked the same way, so no particular use of power can explain this. Any ideas/suggestions are welcome.
