40%~60% condition is recommended when you're not going to use your battery for a long time. If you bring your battery to a charge level of around 40%~60% and store it in a cold place, this will extend its life. I suggest storing it in refrigerator. It’s a good place but don't set the temperature too low, and remember not to fully discharge it to avoid electrolytic spillage. Here are some laptop battery tips that may be useful.
The biggest factor in battery life, especially for laptops, is the temperature at which the battery is kept. Another important thing is, storage or using at 100% charge is harmful. I think you should read this crucial article about "Lithium-ion battery preservation" for further info.