Replacement fuses for BT3554 The Z5050 is a spare fuse set (5 pcs.) for the BT3554 series portable battery testers from HIOKI. The HIOKI Z5050 is a spare fuse set (5 pcs.) for the portable battery testers of the BT3554 series from HIOKI. It contains five Littelfuse type 0216.630TXP ceramic fuses. It is important to use exactly this type of fuse, as other fuses can damage the device in the event of overvoltage.