Should I charge phone overnight or let battery down to a minimum?
Never let it run down below 10% if you can help it. Running down to "absolute zero" harms your battery (and might even render it inoperable – which is why most devices shut-down before reaching that point). Modern LiIo batteries don't suffer from "memory effect", so ideally you'd plug-in a charger whenever possible: "trickle-charging" doesn't hurt them, low charge (less than 5% definitely) shortens their life-span.

For details, please check with...


our battery-life tag-wiki
What can I do to increase battery life on my Android device?
Does constant charging harm my Android cellphone?
Wikipedia: Lithium Ion batteries
our battery tag-wiki
When should I start charging my Lithium battery?
How frequently is it okay to let the battery discharge fully or as low as possible?