HP EliteBook 745 G2 CPU utilization decreases to 70%

[Tom_avia]

Hello,
This laptop came as slow computer. Typically problem are solved after changing HDD to SSD or/and changing thermal paste. But this time I put SSD to laptop and changed thermal paste. Partially problem solved and computer worked faster. But running stress test on CPU first several seconds CPU utilization is 100%, bet later start to decrease and gradually comes and stabilizes on about 70%. You can see it on a picture.
Does not matter, I run it without battery, or with only batter without power supply, or both supply and battery connected. BIOS had reset. No result.
Do I misunderstand something?

[ktmmotocross]

install all updates and optional driver updates

have
same problem when cpu not goes by 53%. after all driver updates, came back to original frequency

[Tom_avia]

Thanks. Installed all updates, all drivers including video and chipset, updated BIOS to newest. The situation became better, 88-90% when CPU fully loaded in AIDA64.
But had to give to client laptop in such state.