[Leica] Hotshoes on cameras w/out batteries

[summicron at bellsouth.net (Frank F. Farmer)]

I found out, not too long ago, that a flash does not work on a M6TTL camera 
if the body has no batteries (or they are dead).  I suppose it was a life 
lesson about carring extra batteries.  So, now I have a couple of questions 
about assessory shoes and flash contacts:  

1) Cameras like the M4-P have hot shoes, but no batteries to speak of.  How 
does such a camera trigger the electrical contact on the hot shoe?  

2) Why was this changed on the M6TTL?  Does it have to do with the TTL flash 
meter?  

3) Will a "classic" M6 w/out a battery trigger a flash in its hot shoe?

Thanks in advance.

Frank
Jackson, Miss.