Stage 1: Apply charging current limit until the voltage limit per cell is reached.
Stage 2: Apply maximum voltage per cell limit until the current declines below 3% of rated charge current.
Stage 3: Periodically apply a top-off charge about once per 500 hours.
The charge time is about three to five hours, depending upon the charger used. Generally, cell phone batteries can be charged at 1C and laptop-types at 0.8C, where C is the current that would discharge the battery in one hour. Charging is usually stopped when the current goes below 0.03C but it can be left indefinitely depending on desired charging time. Some fast chargers skip stage 2 and claim the battery is ready at 70% charge. Laptop battery chargers sometimes gamble, and try to charge up to 4.35v then disconnect battery. This helps to compensate internal resistance and charge up to 100% in short time.
Top-off charging is recommended to be initiated when voltage goes below 4.05 V/cell.
Lithium-ion[which?] cells are charged with 4.2 ± 0.05 V/cell,except for military long-life cells where 3.92 V is used to extend battery life. Most protection circuits cut off if either 4.3 V or 90 °C is reached. If the voltage drops below 2.50 V per cell, the battery protection circuit may also render it unchargeable with regular charging equipment. Most battery protection circuits stop at 2.7–3.0 V per cell.
For safety reasons it is recommended to stay within the manufacturer's stated voltage and current ratings during both charge and discharge cycles.
Device: Nexus One