While the Lithium Ion batteries in most newer cell phones do not have "memory" issues found in older batteries, there is still a memory effect that can occur over time due to the loss of lithium ions in the battery that occur over time. If your battery is suffering from this, you'll find that your battery claims to be charged and then it will very quickly go from a somewhat charged state to nearly dead. This is sometimes referred to as the "virtual memory effect".

To keep this from happening, you need to make sure that on occasion (every 20 charges or so), you allow your cell phone battery to get low enough that the low battery alarm comes on. You don't need to completely drain the battery (this can actually be bad for lithium ion batteries if done often), just get it low enough so that the alarm comes on before you begin charging. If you do this, you'll avoid the virtual memory effect. If you charge your still partially-charge phone every night, you can look forward to having the virtual memory effect in the future.