[Q] quick battery question for noob

Hi guys, I recently rooted my I9300 galaxy s3 and my first ever flashed rom is cyanogenmod 10. Overall I'm pretty impressed with the look and feel, but it does appear to be draining the battery more than than it was before rooting and flashing.

I read somewhere else that no matter what rom you flash, battery drain will always be high for the first few days before settling down to a more acceptable rate. Does anyone know if this is true?

Thanks in advance :)