How much does a battering ram weigh?
That would depend on how big it was made.
A scaling tower was used in ancient wars to allow soldiers to reach the top of an enemies' town or fortress walls. If a battering ram is attached to it, then scaling the walls over an entrance to a fortress or city plus using the battering ram to break open the forts doors can be accomplished. This type of war "machines" were used into the Middle Ages.
As a device intended to knock down a sealed door of some kind, a battering ram is indeed a simple machine; or, at least, it can be. For, while sophisticated battering rams have been created and utilized, the trunk of a tree can serve just as well, when and where the gate or gateway to be rammed open is appropriately sized.
How did the moat drawbridge main gate portcullis gate towers and murder holes each attempt to make it difficult for attackers to use the battering ram?
There weren't many. Besides being slow to move, battering rams were very effective. Battering rams were used to bash down gates, doors, and walls from ancient times to present day. The simplest form of a battering ram could be just a log carried by several men, who would charge at a door or wall in an attempt to break it down. More complex battering rams could be placed on wheels, with a protective roof that…