Make sure the press fitting (the part of the cylinder you can't unscrew) is well seated or it might cause erratic contact with the battery.
Because of the way the electronics in the VAMO5 work, in cycles, it'll fire but your voltage will drop and not show on the LED. Look at the joint, if it's showing more than
a sixteenth of an inch gap, take your
tank off, make sure the beauty ring is on, slap it it hard on the top or bottom, and it'll close the gap.
Also, make sure your battery is a good one. The fact it's showing a 70% charge doesn't necessarily mean it's pushing enough voltage/wattage.
I've had car
batteries show 12.4 volts on a meter but not be able to crank the starter.