1) How long a period does the manufacturer claim the machine can run off battery power? Plus or minus (probably the later) a margin for error?
2) Did the battery fail drastically short of expectations?
3) Was the battery fully charged before hand?
4) Was it checked before the deployment? What do the records show?
5) How has it performed since (has battery performance been analysed)?
6) Did this incident occur in an ambulance? Was no power available within the vehicle?
It sounds to me like someone got either got their calculations wrong, or took a risk (or both) and now people are casting around for something (or someone) to blame!
What if the investigation concludes there is (was) nothing wrong with the kit? Who (or what) are they going to blame then?
You haven't mentioned the patient's outcome. Are we to assume the worst case?

Any third party investigator is likely to end up embroiled in internal politics at the hospital - and possibly beyond (
aka "the blame game"). No doubt people will require the report to be written (slanted) in a particular way. There's no need to travel to Singapore. In fact it's best avoided, by the sound of things!
I would have thought that the money allocated for flying in investigators could be put to better use purchasing some decent batteries, running a few tests, and re-engineering the systems involved (if need be) to ensure that the hospital is not embarrassed again in the future!