If the RAM is half free then will it consume only 50% of power
Nope. RAM uses power no matter whether the cells are used or not.
The biggest consumer of power in a phone is the display (screen), the various radios (Wifi, 3G/4G, GPS, bluetooth, etc), and the CPU and GPU.
ROM is an overloaded term, it is technically an abbreviation of read-only memory, but there is actually no such thing in modern smartphones. The "read-only memory" (ROM) in modern smart phone is actually writable. What most people say when they say ROM depends on the context, sometimes they meant the flash storage (hardware) and sometimes they meant the firmware (software).
In most Android devices, internal and external storage both uses flash storage, so it's should not be surprising that their power requirements are similar. However, unless you're using an application that is constantly reading or writing large amount of data, the power draw from flash storage are generally quite minimal to overall power usage.
Does all this have an effect on battery utilization?
Yes, but on typical use cases, they are not the major power draw. In typical usage patterns, the display and the antennas trumps all other components by miles.