The amount of RAM used has no bearing on battery consumption. Android keeps inactive apps/processes in RAM if possible, but if these aren't consuming processor cycles i.e. working then they use negligible power. Using a Twitter client as an example, it will occupy RAM but if it only polls for updates every 4hrs then it will only become active briefly at that interval and then use the battery. If it happens overnight and the screen remains off the drain will be miniscule.