Why do you need 2 MOPP against the 5V? - Of yourse a current can flow in a battery ooperated device, that's actually what the battery is there for ;-) You have to make sure, that the patient cannnot connect the (-) and (+) of the battery at the same time, eg. with two fingers. In this case a patient leakage current of 5mA would flow which exceeds tha maximum allowed values. Sometimes there are mounting screws or other conductive parts which are accessible to the patient and connected to battery (-) at the same time, e.g. via the mounting hole on the PCB and a common ground. In this case you have to assure, that the patient is separated from the battery (+) with 2 MOPP.
For a working voltage of 5Vdc the corresponding dielectric strength test voltage is 1000V for 2 MOPP, that is correct. But maybe it is possible to apply two independent 1 MOPP with 500V each only? E.g. if you have areas, where you need to protect from the battery (+) or (-) only?
Regarding the creepage and clearance for 2 MOPP. I think the required creepage of 3,4mm is to large. Creepages can be interpolated. In my oppinion it is possibel to interpolate between 0mm for 0V (which is not in table 12) and 3,4mm for 17V (first line of table 12. For 5V you would end up with 1,0mm. BUT: The creepage cannot be less than the clearance, which is 1,6mm (no interpolation possible).
Again it might be possible to seperate the required creepage/clearance into two single 1 MOPP with 0,8mm each?
For a working voltage of 5Vdc the corresponding dielectric strength test voltage is 1000V for 2 MOPP, that is correct. But maybe it is possible to apply two independent 1 MOPP with 500V each only? E.g. if you have areas, where you need to protect from the battery (+) or (-) only?
Regarding the creepage and clearance for 2 MOPP. I think the required creepage of 3,4mm is to large. Creepages can be interpolated. In my oppinion it is possibel to interpolate between 0mm for 0V (which is not in table 12) and 3,4mm for 17V (first line of table 12. For 5V you would end up with 1,0mm. BUT: The creepage cannot be less than the clearance, which is 1,6mm (no interpolation possible).
Again it might be possible to seperate the required creepage/clearance into two single 1 MOPP with 0,8mm each?
I think this section "8.9.1.6 * Interpolation" says that we cannot interpolate between 0 and 17V
