RE: amp draw
There is an obvious difference between ampere "draw" and the battery capacity.
a 600mah NiCad battery might have 400mah or so available.
Current "draw" vs output voltage curve is more to the point.
As the current draw increases, the battery output voltage decreases.
Obviously, if it decreases enough, servos slow down, and receivers may stop working.
Some testing using 2000mah "quality" NMIH batteries showed that they had significant voltage drop
above 1 to 2 ampere draw. There are battery voltage/current charts floating around the web.
It is possible for a failing digital servo to draw 1 1/2 ampere, and still function (but poorly)
(Had it happen!)