INTP:
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 10000mAh source but I'd like to not need 2 always.
What about the boost regulators like I mentioned in an earlier post. There's no reason to boost to a voltage beyond what offers stable operation. Just maybe 7.5 would probably do just fine. And those boost regs are very efficient. Their only drawback is that their output can have enough noise to cause some problems directly powering an audio circuit. But even that is not an issue when you already are powering the board through its VIN pin, and have the benefit of its on board 5V regulator.