Seven people were injured in the incident with terrified consumers spilling out into Bahnhofstrasse, one of the world's most expensive and exclusive shopping avenues.
Specialists from the Zurich Forensic Institute were studying the battery to determine the cause of the incident.
Forensics team have arrived at the scene and are investigating the battery fire issue.
"At the same time, there was a slight build-up of smoke, which led to around 50 customers and employees having to leave the business temporarily", a police statement said. It then began emitting smoke, prompting the staff to throw quartz sand on it to contain the smoke and allow it to be ventilated. "It sprinkled quartz sand over the overheated battery so that the smoke could be contained and sucked out after switching on the ventilation". Six other people received medical care on site - presumably for smoke inhalation - but none required hospital treatment.
The device exploded abruptly when the repairman was examining the device, without any particular reason, said the Zurich police official.