What's the load pattern on a Volt battery look like? It's clearly very different from an ICE car. My last car had a 5.7L Hemi, the battery was in the trunk and lasted 9 years, all of my previous cars went through batteries every 4 years. The Volt only uses it's ICE after the battery is drained so much, if not most, of the time the battery doesn't have to crank the engine, on top of that it's a very small engine. If you are running on the ICE in a city the Volt shuts the engine off at stops which increases the number of engine starts the battery has to do, assuming that's a frequent occurrence for you. I can imagine that the battery life in a Volt would have a much wider variation then it would in a conventional car, for people who are the battery 90% or more of the time the battery by only be subject to time based degradation, whereas someone who does a lot of start stop driving on the Volt's ICE would see a lower battery life.