Thanks for your response. The battery is an EverReady (standard, not alkaline) for lanterns and flashing lights (I bought it at Radio Shack)--it has two posts with knurled nuts to make the connections.

Since D batteries work so well in your experience, I'm sure my set up will pump a lot of water before running out of juice.

It is amazing how this tiny pump (no bigger than a fist) throws out so much water--sure beats the hand pump!