Jstein writes:

Does anyone know the current
readings at the battery at full capacity? Also what is the purpose
for the 3rd contact labeled "T" ?

This would be good to know, but ...

My XTi has two areas of pogo landings at the bottom of the battery
compartment that may be what the AC adapter uses, not the battery contacts
on the side.

The 40D battery has a 3rd and 4th contact besides + and -, and one pogo
landing area.