i have downloaded Racing rivals apk mod from here http://apkfeast.com/2017/12/16/racing-rivals-apk-mod-everything/ going good but draining my battery fast
You downloaded from an unknown app store. It is possible that the app has a virus or other malware that is causing damage to your phone including but not limited to fast battery draining.
Personally what I would do is to back up data, do a factory data reset and only install from trusted sources like Google Play, Amazon app store, etc.
Hallux probably has the answer - most games draw pretty heavily on the battery. Look in your battery usage and you'll probably see the screen and the game as the major users.