You definitely don’t want to be carrying this hacked flash around with you. However, it is a great project for any photographer who is shooting off shoe.
If you’ve been shooting with a flash for a while, I’m sure you had some battery problem or another at least once. Like when one of four batteries goes bad and quickly discharges the other three. Or when it’s cold and the batteries don’t hold their charge so well anymore. Wouldn’t it be nice if you could have a more reliable source of power? One that virtually lasts for ever (well, not forever, but for a darn long time).
More about DIY: External SLA Battery Flash Mod