Some systems do require the battery to run at full speed -- even on AC power;  most Inspirons do not though. Does the system correctly sense the AC adapter power rating (F2 at powerup to check)?  If the adapter shows "unknown", the system will run at low speed all the time. Do not rely on the fact that the system does run on AC as evidence the adapter is sensed -- it will, just not at full speed.  You must check. If the adapter shows unknown, replace it with a new OEM Dell adapter.  If that doesn't solve the issue, the DC input jack in the system is next to replace.  
 Ubuntu performance is low, both CPU or GPU after I removed my Battery of the laptop the issue wasn't there while the build-in battery was still running I tried to instal Dell command on my ubuntu but had no idea how to run it to adjust the performance of CPU of power laptop Inspiron 15 5000 series         [IMAGE]
No Batter Laptop