You can use ThrottleStop[1] to disable PROCHOT on non-standard battery. I encountered similar issue with throttling on my Dell Precision laptop when I was charging it via 60 W USB-C charger instead of proprietary barrel-type 130 W plug. The system triggered a warning about low power charger and initiated aggressive cpu frequency scaling. By using ThrottleStop, I was able to use type-c 60W charger on lightweight tasks (such as web browsing, older games) just fine.
[1]: https://www.techpowerup.com/download/techpowerup-throttlesto...