Toyota has been selling hybrids for a long time now, and the time and mileages that these cars have logged have proven (at least to me, and I was very skeptical) that battery failure is pretty much a non-issue. The charging system does not allow the battery to over or under charge and even in extreme weather, failure rates are very, very low.
I typically keep cars to between 300 and 400K, and believe that a Prius would easily reach those mileages without any difficulty or major expense.
If we had to replace the Corolla today, I'd seriously consider the Prius C.