Preserve entity state instead of unknown/unavailable

[CFenner]

I would like to see the last known value for some entities.

For example I have some devices having a battery. Some of them are always on (iPhone), others go into deep sleep to save battery load (IKEA) and others are integrated using a bridge which I sometimes disconnect to save energy (Netatmo).

For those entities it would be nice to see the last reported state instead of unknown / unavailable.

[KTibow]

You might be able to do this with an input_number and an automation.