Why just 6+? Aim for big.Haha.. ok Sounds good
Anyway.. whats the secret of 6+ hrs of SOT?
Uninstall, disable, use FHD, use 60 hz, use only Wi-Fi, stare at the screen for hours using YouTube, use only one Email Id, don't use location service, don't use cloud services, use power saving, use single Sim, disable mobile data... Voila! you get more than you're asking for.
Basically use it as a feature phone. It's a secret sauce not everyone has the courage to eat.