Good point about the Kanger voltage. I forgot about that.

However, I have some Ego clones that also fire at 3.7, verified on my multimeter. It actually measured at 3.6, but it wasn't fully charged.
Good to hear they fire @ 3.7 volts and thank you.
The Joytech batteries are regulated. The Kgo/Riva doesn't fire at 3.7 volts throughout the charge.
You're right. They fire @ 3.7 "most" of the time. To the OP...you'd might be more happy moving up to a VV Spinner or Twist. Could also use the JoyTech charger on them.