[Q] Battery

Hello, I'm new to this Forum and new to rooting....
Please help me if you can.....
I have a Samsung Galaxy S3 GT-I9300
and the battery after 7 hours is always below 10%, I have the POWER SAVING MODE turned ON..
I'm currently running
MS Team HD 10.0 ROM with android 4.2.1....
please can you help me getting better battery out of it....
If my phone is on standby the it also decreases dramatically....
Thank You....
:(