Continuing to expand my preparations after reengaging photography, the other day I unpacked 3 Sunpak 433D units I had mostly used on light stands for some basic studio type shots. None of them would work...tried a couple different sets of fresh AA batteries but they wouldn't come up. Hoping they would come back to life given enough power / sustained current flow, I looked for but at the moment couldn't locate the 3 AC Adapter power units for them...so I unpacked the Sunpak 510V rechargeable External Powerpak I had left over from shooting my Son's wedding back in the 80's and charged it up for 24hrs...fortunately it took the charge and worked. Then I tried it on each of the Sunpak 433D's and it's power & strong current capability began bringing the 433D's back to life...as if the capacitors had to be massaged with high sustained current to get them going again. The more I kept firing the flash units with the powerful external battery the faster they began to recycle...and after a half hour with the big power unit I tried them again with their normal sets of 4 AA batteries and each of them now work fine again. Saved me from having to lay out a bunch more money for studio flashes...passing along the discovery in case it's of any interest.