What type of gas should normally be used to charge an accumulator?

Typically for a hydraulic accumulator  Nitrogen Gas is used.

Nitrogen gas is recommened to charge an accumulator.

it is the nitrogen gas always used for accumulator

it is nitrogen gas usually used for that type of accumulator

N2 gas is used to recharge bladder accumulators.

Usually the service engineer will carry a N2 cylinder and a charging&testing kit that contains a pressure regulating valve along with the gauge

Nitrogen gas is used to charge bladder type accumulators used in Oil Hydraulics. Nitrogen gas pressure is normally between to % of maximum Oil pressure.