The next step that the technician should take after replacing the battery in the phone is to check the device for malware. Malware is a malicious software that can infect the phone and cause various problems, such as overheating, battery drain, data theft, pop-up ads, or performance slowdowns. Malware can enter the phone through various sources, such as downloading apps from untrusted sources, clicking on suspicious links or attachments, or connecting to insecure Wi- Fi networks. To check the device for malware, the technician can use a reputable antivirus or anti-malware app, such as the ones found in the web search results.