I have a cell phone, it came with a charger. The charger delivers a full amp. This is quite a lot. So much that it a: charges the battery nice and fast, which is useful when you need it, and b: makes the battery quite hot, only nice if you have a cold hand, which in my case is rare*.

Now, heat is one of the things that degrades lithium ion type batteries. Sometimes, I simply don't need to charge my phone super quick. So, put a current limiter on the charger, so you can charge it at 0.1/0.2/0.5A or whatever, if you've got a long time. Thereby preserving your battery.

Later on, this could probably be built into the phone software, so you could tell the phone to be ready by a certain time, for example when your morning alarm goes off. But for now, a standalone charger is the way to go.

* I have loosely coupled mitochondria, that's a northern European heritage for you.
-- bs0u0155, May 06 2013

random, halfbakery