Bluetooth and headphones

Hello everybody.
I have a doubt, maybe some of you can take away this curiosity:

when I use my bluetooth headphones connected to the smartphone (Honor 9 with Android 9) the battery consumption of the smartphone in an hour is almost zero.
If I use the same headphones connected to the lemfo lem 12, the battery consumption in the smartwatch is evident.
Why this difference? could it depend on the fact that there is android 7 on the smartwatch?

Thank you in advance for the answers

I will take a guess that the Honor 9 phone is defective. Have you tested the phone with a different BT headphone? Also, what is the BT software version of the headphone versus the phone and/or watch? Perhaps the headphone has an old BT version.