I'm new to this, but not to lithium battery charging. I fly RC helicopters which run 6 cell (22.2V) lithium polymer
batteries which can literally burn a house down if not handled properly
Never charge lithium
batteries unattended, and never deplete them below about 20% of their fully charged capacity. If you deplete them too far, you will risk ruining the battery, and you will also risk raising the internal resistance of the battery, which causes them to overheat when being charged (and drained). Phones and tablets have lithium batteries, too, but their charging circuits are pretty smart. That said, I left an old iPhone plugged in for close to two years straight and had it mounted to a wall to use as an iPod, and the battery swelled so much over time that it cracked and blew the screen out of it.