According to battery-testing firm Cadex Electronics, a fully charged lithium-ion battery will lose about 20 percent of its capacity after a year of typical storage. Increase the temperature to just above 100 degrees Fahrenheit—as in a hot attic, for example—and that number is 35 percent.
I bought a laptop for work two years ago. At the time I got a nice 5 hours of battery life. Last year, the time dropped to 4 hours. This month, the battery is running out of juice in about 3 hours. A software included in the laptop states that the battery has basically degraded to around 60% of its original capacity.
It sucks but that's just the nature of lithium-ion.
Link via Instapundit.