Track Logs of installed apk in android

Im new to android development. I want to track logs in the testing devices, i googled it and i'm confused pls guide which is the correct

way. 1. Can Log4j be used and save the logs in device sd card? 2. Firebase Analytics can be used? Is that free to use or paid? 3. Or any other tracking solution? Guide me which is the correct way to track the logs. Since my app is based on notifications it behaves abnormal randomly in different versions and im not able to track the log.