Need 2ah capacity, 400v voltage, how to match the battery

You can use a 2AH low-voltage battery, with DC-DC, for boosting to 400V can be, such as 2AH 6V battery with 6V to 400V DC-DC, for boosting to 400V. taking into account the efficiency of the loss, the capacity of the 2AH battery should be higher, some affluent.