In general you have 200 charge/recharge cycles before a battery is near 50% of original capacity. The exact number depends on how you leave it charged. If you leave a Li-ion battery in the discharged state (overnight, storage, you always run it dead), then you are abusing the battery, depending on the time you left it discharged. This is different from most advice from Nickel-Metal-hydride, which can recover some lost capacity by "cycling" the battery. Cycling does not improve Li-ion performance, but does increase the accuracy which it reports (pretty pointless). Consider this, If you drain you battery every day at work, drive home, then charge it, it would be dead (<50%) within a year. If rather you, Go to work, work for 4 hours, charge for 1 hour, then use for 4 hours, then charge on the way home. then after a years time , your battery would be near 80%. And the last is shelf life of Li-ion batteries, say you bought 2 batteries with your laptop, one for use, one extra which is saved for when the first dies. After a years time, given the above scenario, the used battery will be between 50-80%. If the empty battery was left in packaging, then through the years time, it has lost its charge to due 'leakage current', effectly reducing it to storing it at 80-90%. When the battery is stored while not having 100%, chemical decay of the electrodes and the electrolytic occurs (lithium is pretty reactive).
Best case it so use two batteries such that they stay near 100%.
These are just numbers pulled from ether-space guided by rules of thumb,