Zero Motorcycles is recalling all 2012 Zero S and DS models as well as the DSP police bike, because of a problem that can cause an electrical short in the battery, creating a fire risk. Due to the nature of the issue, Zero will be buying back all models from owners, or offer a financial trade-assist towards a newer model. The recall affects 218 units in the U.S.

According to documents released by the National Highway Traffic Safety Administration, the cell pouches in the battery packs of the affected models were designed in such a way that they could move within their holders. Through regular wear, this may cause a breach in the outer layers of the cell pouches. Humidity can thus penetrate the pouches, leading to cell separator decay and allowing an internal short within the cell, creating the potential for what Zero calls a “thermal event” (i.e. fire). Motorcycles affected by this problem may exhibit a significant decrease in power and range.

The problem was first reported in July 21, 2016 after an S model converted for police use in Hong Kong experienced a “thermal event” while charging. According to the South China Morning Post, a pair of S models were charging at the Ngau Tau Kok police station when one of them caught on fire at 1:15 am local time. The fire damaged both motorcycles as well as a nearby police van, but no one was injured.

Zero hired a battery technical expert to examine the affected motorcycle as well as the rest of the police department’s fleet. The contracted expert determined the cause was due to unexpected wear of a cell pouch combined with the humid Hong Kong climate. Zero proceeded to notify the cell manufacturer, Energy Innovation Group (EIG). The South Korean company responded, saying it had received no other reports and could not recreate the problem.

Fast forward to October 2017 when Zero received two more reports, one from Canada and another from Texas. In both of these cases, a 2012 Zero S model experienced thermal events. Both Zero’s battery technical expert and the contractor that conducted the Hong Kong investigation conducted a forensic analysis of the two North American bikes but were not able to make much progress due to the extensive damage to the two bikes. Zero’s battery expert conducted further analysis on battery packs that had been returned to Zero from customers and found evidence of wear on the cell pouches and signs of humidity entering the pouches. According to Zero, EIG did not respond to requests to take part in the analysis.

The problem only affects 2012 Zero S, DS and DSP models. For the 2013 model year, Zero changed to a completely different battery pack architecture produced from a different supplier that uses cells fixed within their holders and thus will not experience the same wear.

According to Zero, EIG had not made any changes to the design of the battery pack architecture, so there is no remedy in place. As a result, Zero will repurchase all 2012 S, DS and DSP models or offer a financial trade-assist towards a newer model. Zero asks owners of affected models to avoid riding or charging recalled units. Zero will arrange to pick up all recalled models at no expense to owners.