Help how can i get notifications when in locked mode on samsung galaxy s3?

[sealover1]

hi guys how can i get notifications when in locked mode on samsung galaxy s3?
I get emails notifications when its in locked mode and the charger is pluged in but soon as i unplug it my notifications stop
I,m thinking theres some sort of battery saving thing on somewhere but i cant seem to find it lol
cheers for any help