The company should have access to a report from Nationally Registered Testing Laboratory like UL or Intertek that tested their product and supports their claim. If he has the leverage to do so, he should get them to provide him with that data. If they are a legitimate company that has been around for any length of time, they should have that testing. Without that testing, they might as well be a knockoff with an unpronounceable name you purchased from Amazon. Without that data, I would not take the developers word for it - even being perfectly honest, he has no idea what those batteries will actually do without testing having been done.
It would behoove them even make it available on their website, unless they want to go through this in every jurisdiction they want to have their products installed in.
It could be that the technology is new enough that there is not a test standard that really applies. In which case, I think you will be out of luck looking for good documentation.