Using DC-DC-step-up and DC-DC-step-down converters

I'm interested in hearing what the methods are for running an Arduino on 6V 5Ah SLA. I just scored a dozen or so of them at $2 a pop and they are rechargeable. Running 2 in series and then bucking to 5V is one option that gives a 5000mAh source but I'd like to not need 2 always.

fix'd