Double check the CPU is still running at full speed. Without a battery most mopdern laptops will throttle CPU (and maybe GPU) performance.

Also there’s no reason to remove the battery if you can cap it’s charging. 80% is better than 100%, but if it’s plugged in 24/7 cap it as low as it will let you. But 60% is even better than 80% for health. And any cap below 100% severely reduces the chance its battery will expand.