Från BatteryUniversity (http://batteryuniversity.com) :
"... 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 ..."
Och så vidare, se deras "Part One", "Part Two" samt "Part Three" för fullständig info om diverse batterier och deras egenskaper.