Well I had a mishap with my Grand using a 510 extension so I could use my map tank on it.I was using a AW IMR 18650 and I guess the connector shorted because my spring glowed red and shortened a bit lol.Needless to say I was ...... and won't be using any connection,extensions etc. ever again.My 18650 was too short to make spring contact after that so i put 2 AW ICR123 750mah protected batteries in it from my Joker mod.I screwed my digital meter on and it measured 8.4 volts.I never vaped over 6.5 volts before so I didn't know what to expect.I put one of my Ikenvape HV 306's that were dewicked and debridged on it and gave it a try.All I can say is wow what a great vape.I'm vaping KBV Monkey Bread 60/40 12mg and it tastes awesome.The hit duration is about 1 second and it gives huge vapor,taste,and throat hit with no burnt taste at all.Not sure how long the 306 will last at this voltage but I will let you know.If all my juices are this good at 8.4 volts bye bye LR attys at 3.7 volts.