Brightness

When 2 battery is connected in series with a light bulb, the brightness of the bulb is as follows:

When a similar light bulb is connected in series, the brightness changes to the following:

What happens if the same light bulb is connected in parallel to the existing light bulb instead?

PREDICT and EXPLAIN ! 

When 2 similar additional batteries are connected in parallel to the existing batteries, the brightness is as follows:

What happens if the 2 similar additional batteries is added in series to the original batteries instead? 

PREDICT and EXPLAIN !