Just a thing about Li-ion batteries. It's not a good idea to discharge them completely. When doing that you corrupt the fuel cells and with time loose battery capacity.
Here's some useful info:
How to prolong lithium-based batteries
QUOTE:
A lithium-ion battery provides 300-500 discharge/charge cycles. The battery prefers a partial rather than a full discharge. Frequent full discharges should be avoided when possible. Instead, charge the battery more often or use a larger battery. There is no concern of memory when applying unscheduled charges.