I have been thinking about an external battery for my flash for quite a while. My main flash (Sigma F-500 DG Super) doesn't have a high-voltage power connection, and anyway high-voltage batteries are rather pricey for my not so often use... So I haven't done anything with that until I found the post on shutterbug.net last week.
In the nutshell that post explains that using external low-voltage low-cost high-capacity sealed lead-acid battery (6V 4-4.5Ah) helps to reduce re-cycle time significantly for many flash models. While I didn't see such batteries in the shops in my neighborhood there were plenty available via ebay, with the price around 10 Eur (plus delivery). So I ordered my battery last week.
Incidentally there was a post on Strobist on the same subject just the very next day after I ordered my battery. While the main post was about high-voltage batteries, the reader's comments discussed low-voltage option as well, and there was reference to the same shutterbug post made in the comments.
Now about my own results:
I have bought 6V 4.5Ah lead-acid battery (about 20 Eur including delivery).
- It charges my Sigma EF-500 DG Super for ~1.5 sec at full power (vs ~6 sec from AA batteries).
- My old manual thyristor National flash (pe-3066g) also charges much faster than before (around 3.5 sec).
- However my Sunpak 4000AF isn't any faster - I suppose it has a current limitation circuit, so it still takes about 9 seconds to charge...
I bought a little bag for 3 Eur that just perfectly matches the size of the battery; and I spent 2 Eur for the contacts in car accessories shop. I found some wires at home, so I soldered the contacts to the wires. Also I spent about 20 Eur for charger, but any AC/DC transformer or motorcycle charger that can produce 6.5 V 1.5A current will do the work.