using buffered bitmaps and battery/performance

Before I'll make test maybe somebody knows answer.

Is this 2 cases equivalent (battery/performance), drawing (of course the same drawing and clearing buffered bitmap before):

1. directly on screen;

2.

A. First on buffered bitmap than

B. drawBitmap;

I feel 1 should be better but maybe drawBitmap is very fast, made by system so it compensates for drawing in 2 stages.

Of course if drawing only B. because drawing didn't change should be better.