When a battery company unveils new technology and brags about its long lifetime, the best industry analysts aren’t necessarily impressed by charts showing voltage-current curves over hundreds or thousands of discharge cycles. “Show me the warranty,” they say. That’s a good indication of how long the company really thinks the battery will last.

GM executives have said they expect the battery for its upcoming Volt electric vehicle (actually, a type of plug-in hybrid) will last the life of the car. Now GM has backed up those claims (sort of) by announcing a 8-year, 100,000 mile battery warranty. That’s not quite as long as I’d like a car to last–and not as good as a 10-year warranty some had expected–but it’s a good amount of time compared to the 3-year warranty offered by some other manufacturers. Nissan, which is coming out with the electric Leaf this year, hasn’t yet announced warranty details.

The battery warranty is key, since replacing a full battery pack could cost more than $10,000 by some estimates.