Newer ThinkPads make use of high performance CPUs that may require more power than what the 65W adapter can provide while also supporting USB, Optical and other attached devices, especially in docked configurations. To prevent the potential for sudden system shut down if the power demand exceeds what the adapter can supply, the maximum clock speed may be limited when the system is operated on the 65W AC adapter and no battery is installed.
The following ThinkPad systems may be affected by this symptom:
If maximum frequency operation is preferred in such situations, a 90W AC adapter should be used. Additionally, operating with battery in circuit offers additional protection of data in the loss of AC input power.