Fully charged capacity declines as the battery pack ages, with the number of charge cycles, amount of time at full charge, and time at high temperature.
Under average usage patterns your battery maintains approximately 70% of its power capacity after the first year of operation:
: Percentage (%) - Full Charge Capacity / Design Capacity x 100
Each time the battery discharges a total of 85% and recharges counts as one charge cycle (e.g. discharging 45%, recharging, discharging 40% and recharging is 45%+40%=85% one cycle) .
It is beneficial to periodically reset the battery gauge. This allows the computer to more accurately estimate full charge capacity. To reset the battery gauge in the Power Manager, click on Battery Maintenance then Perform Reset. This will require you to let your battery run completely down, and then to recharge it fully.