Your ThinkPad battery is a "consumable" product that decreases in performance over time. However, there are several things you can do to improve the performance and the life of your battery.
1. Do not place your battery or your ThinkPad in a high temperature environment, such as a car on a hot day. This will permanently damage the capacity of your ThinkPad. You may damage it even more if you charge the device in these temperatures. Even storing a battery in a hot environment can damage it irreversibly.
2. Battery Performance will be temporarily degraded if used in a cold environment.
3. When you store your battery outside of your ThinkPad Computer, store it with a charge of less than 50% to reduce the battery wear. If you store a battery when it's fully discharged, it could fall into a deep discharge state, which renders it incapable of holding any charge. Conversely, if you store it fully charged for an extended period of time, the battery may experience some loss of battery capacity, meaning it will have a shorter life. Be sure to store the ejected battery at the proper temperature
4. Recondition your battery by letting your battery run to less than 3% at least once a month. Reconditioning the battery can restore some of your battery capacity. Using included software such as Power Manager can make this process even simpler, and will remind you when this cycle needs to occur.
5. When the computer uses a large amount of electricity from the battery, the temperature of the battery and the computer may rise. In this case, the battery might automatically stop charging so that the battery operates at a level that ensures comfortable usage and normal battery life. If the battery has stopped charging, it might not start charging immediately when you plug in the AC adapter or it may take more time to completely charge. When the battery is restored to its normal temperature, the battery will start to recharge.
6. Brightness: Dim the screen to the lowest comfortable level to achieve maximum battery life. For instance, when watching a DVD on an airplane, you may not need full brightness if all the cabin lights are off. Wireless: Wireless network adapters consume power, even if you are not using its features to connect to a network. You can turn wireless off in the control panel to save power. CD's: Having a CD in your CD drive, even if it is not in use also consumes battery power because the computer will constantly verify the presence of a CD. Remove CD's when not in use for extended battery life.
Under average usage patterns 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. For instance, you could use your laptop for an hour one day, using half its power, and then recharge it fully. If you did the same thing the next day, it would count as one charge cycle, not two, so you may take several days to complete a cycle. Each time you complete a charge cycle, it diminishes battery capacity slightly, but you can put laptop batteries through about 300 full charge cycles before they will only hold 80% of original battery capacity (if the battery is properly maintained). 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.
(Information taken directly from IBM's Knowledge base)