On average, you can use Melomania 1+ for up to 9 hours on one charge, with a further 36 hours within the charging case depending on usage.
If you experience notably lower battery life than this, there are a few things you can check:
Firmware
Always ensure that the earbuds are running the lasted firmware version (V9.0.1) first. This should ensure that the earbud's performance is not affected by known issues and bugs.
High volume levels
Higher volumes require more power to drive the speaker inside. Reducing to a lower level can prove beneficial for your hearing and extend the use of the earbud.
Always using one earbud as the master version
Swapping the master between left and right occasionally will ensure that one earbud does not deplete at a faster rate than the other.
Using the highest possible codec
Using AptX or AAC may deplete the battery quicker as more data is being transferred between your device and Melomania 1+. If you can restrict your device to SBC only, you may experience longer listening time.