[DCD 985 make same power on small 1.5 ah as 3.0ah?]

3.0 amps sounds like nickel metal hydride, is that what your using?

[Does a larger battery give more POWER? Results inside...]

I missed in your intro that you got the larger batteries second hand. That should play into the results somehow. I know that nicads develop an unchargeable area over time and tha has a huge impact.

[Does a larger battery give more POWER? Results inside...]

I would think the real test is how many holes are rilled and how many screws are driven. The speed is a function of the gearing etc while the longevity is a function of the available power (amperage).