To reduce the resistance in the battery cells, put smaller patteries in series.

Ideally the resistance of the load will match (or be higher) than the resistance
of the battery pack.  You would have better luck if you replaced each D cell
with four AA or AAA cells in parallel.

You may even be able to make up for some of the losses by building your cells
into a 6v pack and using a switching power supply to up it to your needed
voltage.

-Adam

Sean Breheny wrote:
> I would prefer not to use NiCds for this because it is a one-time
> application. However, I might have to (due to their lower internal R)
> because I found that even a pack of 8 D-cells (in series) drops by about
> 1.5 volt when drawing the kind of current this needs.
>
> Any other suggestions?

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