Replacing car batteries are a fact of life. It can be a real pain, depending on the type of car you've got, but these days batteries seem to last a good long time. So how long is long enough when your car runs exclusively on batteries?
Apparently GM thinks 8 years or 100,000 miles should be enough to assay the fears of early adopters for the Chevy Volt; they'll be providing that warranty to all Volt buyers for their batteries—even Canadians will get the same warranty when the Volt goes on sale there in 2012. It's a bold move that should help set a standard for other would-be EV makers.
The Chevy Volt may or may not be the salvation of General Motors. That said, GM has invested a LOT of resources into ensuring the Volt has a successful launch. They are planning to produce just 30,000 Volts in the first year, with production gradually ramping up if the car meets with commercial success. GM has conducted over 1 million miles of testing on the Volt, including crush tests, water submersion, cold, heat, and rough road testing. And they are confident enough to offer quite the warranty on the battery.