Comparing the Oral-B CrossAction Power Series of Battery powered toothbrushes

The Oral-B CrossAction Power Series of electric toothbrushes are all powered by an AA battery.

a) How does Oral B Cross Action Power work?

b) How to replace brush head of Oral B Cross Action Power

c) How to change the battery of Oral B Cross Action Power 

These series uses the following type of replacement brush heads