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.
For example if you use 25% of the battery and recharge it on 4 occasions, that resulted in 1 cycle of the battery. Using 75% one time and 50% another time would count as 1.25 cycles. This means that lithium batteries start to wear out as soon as you begin to use them. Keeping them plugged in all the time does not count toward the cycles because the circuitry in the charging system bypasses the battery completely when it is fully charged and on AC power.