small battery

Probably work fine, depending what your big secret device is.

.... Phil

I see it all the time, but I'm still amazed by the number of questions that show up here without the slightest hint of specification required to attempt a well-reasoned suggestion.

This elicits the firestorm of suggestions followed by the inevitable name-calling fest. Are we having fun yet?

My answer to your question is, "Can't be done." But that's according to MY definition of "small" and MY assumptions about run time.

Perhaps, you could be influenced to disclose YOUR definitions of "small" and your desired run time. Did you really mean 0.5V -2A? and does that mean it's a current sink? or??? What accuracy/stability is required?

Reasonableness of the answer is highly dependent on the specificity of the question. Your question ain't got none.

"mike"

Makes the solution a bit more complicated...............

Shame how so many OPs post entirely in meaningless generalisations.

Means that is how they are thinking too.

..... Phil

For starters, are you saying the wall-wart reduced 120V AC down to

If you get a Peltier cooler, and heat one side while applying a flow of air to a heatsink on the other side, it will put out low DC voltage at high-ish current. Into the right kind of load. So, that'll work from any battery that can heat a resistor and maybe run a coolling fan.

Well, you DID say 'any thoughts'.

Seriously, do you have any accuracy requirements? AC or DC? Any preference on battery type (palletload of lead/acid, or single hearing aid cell)? Duty cycle? Battery life under load?