Q: Why if the batery for my MacAir is not connected, even if it has the power supply connected the machine runs slower.?

Some moths ago, my battery died, and while buying the replacement I used my Mac Air

with direct power, and I noticed that runs slower.

This week the machine start to run slower, and when trying to find why, I found that

the battery was off, the problem was the connector, and after press the connector

again, the speed was normal.

Is not clear to me why if using battery the machine is faster than with direct power.