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I have a Thinkpad T520 and I'm monitoring my CPU using CPU-Z.

For some reason, when I detach the battery, the CPU only run till 800MHz. Whereas when I run using battery power, it goes up to 2.3GHz. I notice the difference in speed when I take the battery out. This is the reason why I investigated in the first place.

Any ideas on what's going on?

Windows 7
Thinkpad T520
Core i5-2410M
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This behavior is by design. Without the battery, the laptop's power management system cannot accommodate power spikes that occur when the CPU goes from a halted state to an active state. The laptop is simply not designed to operate without a battery.

You might get away with it with some power supplies. But the laptop is simply not designed to work that way. The battery acts like a cushion to make up temporary power shortfalls.

Why do you want to do this anyway? There's likely a sensible way to do whatever it is you want to do.

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My guess is that the BIOS is set up such that it runs slower with the battery removed.

(Of course, whether this is just a glitch in the BIOS or intentional is hard to say. It could be that the power supply is not strong enough to "ride out" brief surges in power demand, or it may be that the power supply relies on the battery to provide filtering.)

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Seems like the power adaptor is underrated for the laptop

If possible, try with a power adaptor one size bigger, i.e. if the current one is 65W, use the 90w one.

(or, the 135 watt one)

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