I find it hard to explain because my need to 'recharge' is so deep and innate I find it difficult to deconstruct and understand
When I have been in situations when I have had minimal peace or privacy, I can't tell what it is to close a door and take a nap, read a book or simply have a shower. Having that door closed is the most incredible relief. I have recurring dreams where the wall of my bedroom are glass and everyone can look in or I am naked in public. This is what it feels like to not have 'recharge' time. I can't actually think efficiently or effectively. My brain needs a period of time of minimal stimulation where I can collate information received and make sense of things.I become resentful if people take this private time away from me even if its unintentional. It feels so invasive - like someone rifling through your personal things.
I'm not sure how an extrovert can be expected to easily anticipate the time when recharge time is needed. And it is unfair if introverts should expect you to always know. But there are some circumstances that it commonly follows. Going to a party or spending several days with relatives etc will require at least one recovery day. Sometimes we just want to do nothing for a while, not necessarily requiring private alone time. We usually will go off and seek out alone time where necessary - we don't expect you to psychically know when to back off. We just withdraw and go for a walk or surf on the net or read a book etc. If you want to do something together or are uncertain as to whether interruptions are welcome, just ask. If your partner wants to go for a walk, ask whether they just want to go alone or whether they want company. If you learn to recognize the sorts of activities they like to do alone and make them feel free to seek them out when needed, they will be very grateful and appreciative. This may even lead to more closeness between you both.