Third post - let's talk about charging and charging frequency
It's important to note that lithium ion cells do not suffer from "memory", which is a loss of capacity from partial charging.
A couple small charges throughout the day, to keep the battery above that 30% threshold is better, overall, for a lithium ion battery, then letting it go below 30% and receiving one big charge at the end of the day.
Another interesting facet of lithium ion battery technology is just as the bottom of the charge profile is hardest on the cells (eg. discharging them down to the very bottom of their capacity), charging to 100% is actually stressful for the cells as well - putting that last 10% of charge into a device is the roughest phase of the charge on the cells. So you're actually best off to always have the device above 30%, but below 100%.
In practical terms, this is hard to do and requires too much monitoring - so the best compromise is to aim for a 100% charge once a day at most - this is the overnight charge originally asked about. You don't want to keep stuffing the battery with that last 10% charge over and over throughout the day, because that's where a lot of the harm and degradation of the battery occurs.
Batteries should be charged when the phone is at room temperature - charging below room temperature doesn't damage the battery (to my knowledge), but charging at an elevated temperature (eg. after an epic gaming session) is an extremely good way to damage the battery. A few full recharges at an internal battery temperature of 40 Celsius is a good way to permanently knock 10-20% capacity off the battery.
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-Scott
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