can crystal be charged by indirect sunlight or candle?

[FairyCrystal]

I'm wondering why you think they need to be charged to begin with? Do you expose them to hard work that could drain them, is there a lot of negativity (stress, conflict, negative thinking etc) in your house?
Do you program your crystals so they get drained?
In short: what is the reason they need charging?

You do not have to put crystals in a circle together to have them work together or charge each other. I have over 300 crystals spread out in my home. They are all connected and have created an energy field that protects me, my home, and also allows them to further open and activate (even though they're all high vibrational anyways), or simply 'be' and do their own thing.

You can put crystals in a circle or any form which is making a grid. but this is usually done to work on a specific thing for which you then program the whole lot.
If doing that, always tell the crystals to not use more than 80% of their energy for that. (Or less if you feel that's better). That way they never drain themselves as they can use the remaining energy to keep charged and happy.
Also, do not forget to remove programs when done AND always ask the crystal if it wants to do that specific job for you.
Some crystals don't, they should be allowed to do their own thing (at that moment) which also benefits you.

Elements can of course make your crystals happy! Being outdoors in the garden, on the soil, in daylight, bit of wind etc etc.
Depending on how high vibrational your crystals are or not, it will do them good. If need be they can charge that way, and if no need for that, they can just enjoy, further open and activate if they're ready for that and so on.

The suggested rinsing off and smudging is not charging, it's cleansing/decharging. Of course if your crystals aren't in good shape for whatever reason and that's why they need charging, it is good to cleanse them properly first.
And sage only removes the mental layers so it's not a thorough cleansing really. Personally I always feel most stuff that you'd want to cleanse is emotional for which you need water. But it won't do any harm to do both of course.

Direct sunlight can be okay, but so is full moonlight. Personally I prefer that as it's nice and gentle, feminine, not forceful etc.