The 4 AA batteries that all flashes take is enough for most uses, but if the flash is not easily accessible, or batteries die too quickly then AA batteries are not a good option any more. I’ve been thinking about how to extend the power supply of flashes.

My solution is to use Li-Ion batteries, with a DC-DC converter. I’ve identified several DC-DC converters that may work.

The big question is how much power does the flash draw when recycling after a flash? On 1/4 power, a SB800 will get about 1500 shots on a 2000mAh battery set. (source) It took 30min for the batteries to reach 1400 shots (and dies at just shy of 1600 shots), so that averages out to about 1 Amp continuous draw out of the batteries for 1/2 hour.

At full power, on a Canon 430EX II, the power draw peaks at 9Amps, then 6Amps after 1 sec, and 3Amps after 2 sec. (source post #15)

For a reasonable price ($12ish) a 5V, 5A DC-DC converter like this one or this one would probably work. The max input voltage is only 14V, so realistically only a 3S Li-Ion battery would work. That’s already twice the voltage of 4 AA batteries.

A bit more power to 10A at 5v can be had for about $18 in this module, or this one.

For higher input voltage range (9-28V) something like this can be used with the limitation that only 2A can be drawn. This one also costs about $24.

Of course there is an option for high input voltage (18-36v) and high output current (40W, so at 5A, that’s 8A) but it also costs $87 in this module. Out of my price range.

I think the best option is to have the max available current any time I need it, even though I may not shoot at full power very often. It also means the re-charge rate is maintained at the same level for a much longer period of time.

A 5000mAh 11.1v (3s) Li-Ion battery from HobbyKing costs about $25. This battery should have more then four times the capacity of 4 AA at 2000mAh.

Is it worth it for the extra complexity? I don’t know.

UPDATE:

Found a DC-DC converter (LMZ12008TZ) for a reasonable price that can handle 6A at anywhere from 0.8V to 6V output. The input voltage is 6V to 20V so a 5s battery would work. The digikey price is $22 ish and it requires very few external parts.