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?

https://www.youtube.com/watch?v=D3AmW9_RZ8w

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

https://www.youtube.com/watch?v=ike9EtZCyws

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

https://www.youtube.com/watch?v=tr_Q-KCtIKo

These series uses the following type of replacement brush heads