Batteries are a "consumable" product and battery life decreases over time, depending on how the battery is used. Over time, the Full Charge Capacity, or total amount of charge the battery will accept, become less than the Design Capacity, or the amount of charge that a new battery can store. Both of these are measured in Watt-hours (Wh) and are displayed in the Battery Information window.
Under average usage patterns (see figure) your ThinkPad battery maintains approximately 70% of its power capacity for the first year of operation. Average usage is defined as the number of recharge cycles. A cycle is defined as each time the battery discharges a total of 85% or more and is recharged it counts as one cycle. The battery health utility uses Design Capacity, Full Charge Capacity, Cycle count and the normal aging properties of your battery to determine your battery capacity status.
X axis : Year
Y axis : Percentage (%) - Full Charge Capacity / Design Capacity x 100
Use the proper AC adapter for your ThinkPad computer. There are several types of AC adapters for ThinkPad, 56 watt or 72 watt. If insufficient power is supplied to your battery, the full charge capacity will appear to be reduced.