The best way to charge a Li-ion battery is to charge at 1C. That means if your battery is 2500mAh (milliamp hours), then you should charge it at 2500mA (milliamps). This will take about an hour, depending on the capacity of your battery.
Once your voltage reaches set maximum (4.0V for most batteries), keep the voltage constant for one more hour for full charge (optional).
After that, you can use your battery up to 4.1V – keep it on the shelf for a week or so.
Keep it up to 4.2V if you need it right away – use it within a day or so.
If you don’t plan on using the battery for a while, charge it up to 4.3V – only use it once every few years and maybe even fewer times than that!