Default [Q] ROM residue after flashing stock firmware?


I've been playing around with ROMs. And I might have flashed things that I shouldn't have flashed. Like modem files and stuff.
My phone is working, but I have erratic battery drains. Like 0.6%/h and the next percentage is 25%/h (screen is off), which I hadn't had before.
I bought a new battery because I thought that might be the problem, but the problem is still there.
So I was thinking that I may have flashed some wrong things like modem drivers that might cause the modem to use too much power.

I did flash a stock firmware. But does this include everything I could have messed up? Or can there still be some residue from other ROMs somewhere? (Kernels, modems, ....?)