We only use the phone as a reserve and rarely use it. When switched off, there is hardly any self-discharge even over several months. Switched on, it certainly lasts for several days.
there's no general answer to this because it depends on the usage: the more whatsapp and/or (slow!) surfing, the more battery consumption. for "normal" use (some whatsapp, no surfing, a few short phone calls) I would say: at least 1-2 days.