Is slow charging bad for the battery? I know that charging the battery too fast can overheat the battery and shorten battery life. But is charging it slowly, e.g. from a USB 2.0 cable plugged to a laptop, also harmful for the battery? I know there is a 'USB charging mode' designed for this, but I am not so sure if it is bad for the battery.

I have Googled, but most links are forums where people offer their opinions and personal experiences, I want to know whether someone has actually tested this out?
Slow charging is great for a lithium battery. Two things kills lithium batteries


Temperature
Charge level


Charging too fast causes excess heat, that damages lithium batteries
Keeping your battery charge too high also damages lithium batteries



Ideally you want to slowly recharge and keep it between 20% - 80%. Also, many short small charge cycles is better than a lengthy large charge cycle.

Sources: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries