1/4 Charged 1.200-1.220 1/2 Charged 1.230-1.250 3/4 charged 1.260-1.280 Fully Charged Battery Charging While the battery is charging it vents highly explosive hydrogen gas ( Hindenburg , anyone?), so adequate precautions must be taken. The battery must be charged in a well-ventilated area, away from any source of flame or spark,