Storing and using data that is only 'live' available at specific times (OralB Battery state)

I think like more people here I may be happier with the OralB Bluetooth integration then one may have thought when it was announced :sweat_smile:

With the recent addition of being able to also read the Batterystate in Home Assistant I would love to also always be able to view my current battery level. With this being Bluetooth the state is only available when the toothbrush is on.

In my ideal situation I would use one variable in my Dashboard that would show either the live battery state or when the brush is off show the last know state. I may in theory also want to use it in automations, but atm I just have an automation setup warning me if the batterystate is bellow a level while brushing.

I can imagine I am not the first, nor this being the first of these types of usecases. So wanted to ask the community what are some of the best / easiest ways to approach this?