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:

ThinkPad Edge 13", E30

ThinkPad Edge E120

ThinkPad Edge E320
ThinkPad L420

ThinkPad L520
ThinkPad R60, R60e, R61, R61e 

ThinkPad R400, R500, T400, T500 
ThinkPad T60, T60p, T61, T61p 

ThinkPad T410, T410i, T410s, T410si, T510, T510i

ThinkPad T420, T420i, T420s, T420si, T520, T520i
ThinkPad W500, W510, W520

ThinkPad W700, W700ds, W701, W701ds
ThinkPad X1

ThinkPad X61, X61s, X61

TabletThinkPad X121e

ThinkPad X200, X200s, X200, X230

Tablet, X300, X301

ThinkPad X201, X201i, X201s, X201 Tablet

ThinkPad X220, X220i, X220 Tablet


 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.