I took this from
Northeast battery.
Manage the Discharge
Recharge your batteries before they are completely dead. Not letting it die completely will extend the battery lifespan.
If you are preparing to store your batteries for a period of time, make sure you do so at half charge. Unlike other types of batteries that need to be recharged throughout their storage time, lithium batteries do better at 40%-50% DOD (depth of discharge).
Pro-Tip: After every 30 charges, allow your lithium based battery to completely discharge before recharging. This helps to avoid a condition called digital memory. Digital memory can mess with the accuracy of the power gauge of the device you’re using. By allowing it to discharge completely you will allow the power gauge to reset.
Some companies disagree with discharging them completely to avoid digital memory. They claim it doesn't exists in lithium's. I do know nickel metal hydride has an issue with this.
What everyone does agree with is, depending on which lithium battery type, they all have a limited number of cycles (full discharge). An example would be a battery rated at 300 cycles will go 600 cycles if not brought below 50%. They also agree about long term storage, you want them around 50%, not fully charged.
They also say, if left at zero for a long time, you can kill them. Not sure how much time "long time" is though.