Even if you’re not able to “read” a schematic, most DIYers can glean a little info. Like is the thermal sensor in the battery or the controller? Something to let you walk through the problem. I have good power. Step one. From there I know nothing. Does it go through a “boot up” system check. I’d expect a failure of such would generate an error, not a blank screen, but I don’t know. Which terminals on the battery are SUPPOSED to have power and how much? If your business model is consumer maintenance, give them the info they need to do it.