Websites for Nikon and Canon have each published warnings about potential problem with cheap counterfeit batteries that are sold in various countries around the world.
The problem with many of these batteries is that they can’t withstand the heavy power demand of modern, high-energy devices. In a best-case scenario, cheaper batteries will reduce the number of images the device can record. A worst-case scenario would result in damage to the camera or injury to the person using the camera or charger.
A statement on the Nikon Europe website (https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/45066/kw/counterfeit) says: Nikon bears no liability for accidents or damage that occurs as a result of the use of counterfeit batteries. The site provides information on how to identify batteries that may cause problems.
Canon USA has dedicated part of its website to identifying and avoiding purchasing counterfeit batteries. Go to http://usa.canon.com/cusa/about_canon/standard_display/avoidingcounterfeits?WT.mc_id=C201981 for full details.