Neewer TT560 made by Godox

A few years ago I purchased a TT560 flash, dirt cheap (25 € if I recall well). It runs on 4 x AA batteries, alcaline 6 Volts, or Ni-mH, much lower voltage but larger current. It's a great flash for the money. I use it in optical S2 slave for backgrounds. Trouble is, it recycles too slowly to keep up with my main flash, a Godox V860 with a 12 Volts Li-Ion battery. That's why I have tested the TT560 on 2 x Li-Ion 18650 batteries from a dead laptop. That's 7.2 volts nominal, and a lot less internal resistance, i.e a lot more current. So far so good. Recycle time is incredibly short, with no sign of overheating. It remains to be seen if it's ok in the long run.

Most of the recycling occurs well below 5V, to deliver on the order of 60 joules. Hence, current is everything and peak voltage is nothing as far as capacitor charger. As long as the control electronics is fine with 7+ volts, I think all is ok.