Lithium-ion batteries these days do not have a memory effect, but will degrade when kept at 100% charge because the internal composition of chemicals will change, destroying the battery in the process. The ideal charge is between 20% and 80%. With (better) battery charge control you can extend the design capacity (the maximum charge the battery can hold when new) and lifespan. With AC attached, the battery will discharge but it will be charged when the minimum charge level is reached.