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It's best to not make it a habit to completely drain a battery. I've heard once a month is ideal. But not always.
 
Just use your phone as you use it. Plug it in, use it all the way, it makes no difference anymore.

Essentially this is the right frame of mind. Focusing on long-term battery health is an unncessary burden unless you plan on keeping this phone 2+ years.
 
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