Laptop Batteries
Types of Batteries
OLPC is using two battery chemistry's from 2 vendors: NiMH, and LiFePo4 batteries. The LiFePo4 batteries allow charging at higher temperatures. The NiMH batteries cannot be charged above about 45 degrees C.
Our batteries vendors are Goldpeak and BYD.
GoldPeak provides both NiMH and LiFePo4 packs.
BYD provides only LiFePo4 packs.
Each chemistry and manufacturer have slightly different specifications.
GoldPeak NiMH
Typical capacity： 3050 mAh
Minimum capacity: 3000 mAh
Only 80% of this capacity is usable
Operating Voltage Rage: 7.5V to 5V at 0.2C discharge current
Operating Temp Charge: 0 ~ +45°C
Operating Temp Discharge: -20 ~ +50°C
Standard charge rate: CC-CV .1C Special NiMH Charging System
GoldPeak LiFePo4
Typical capacity： 2900 mAh
Minimum capacity: 2800 mAh
Operating Voltage Rage: 7.3V to 4V at 0.2C discharge current
Operating Temp Charge: 0 ~ +60°C
Operating Temp Discharge: -20 ~ +70°C
Standard charge rate: CC-CV .8C up to 7.3V
Max charge rate：1.5C（4200 mA）
BYD LiFePo4
Typical capacity： 3150 mAh
Minimum capacity: 3100 mAh
Operating Voltage Rage: 7.5V to 5V at 0.2C discharge current
Operating Temp Charge: -10 ~ +50°C
Operating Temp Discharge: -20 ~ +55°C
Max charge rate：1C（3150 mA）
Lifetime requirements for all batteries
Ambient Temperature：25°C
Number of Cycles：2000
Remaining Capacity after 2000 cycles：50%
Special NiMH Charging System
In order meet the 50% available capacity at 2000 cycles requirement a special charging and discharging system is used for NiMH. Since the "full" charge voltage of an NiMH varies based on temperature, internal resistance, and charge rate all of these parameters must be tracked during the charging cycle.
NiMH cell life is significantly affected by the maximum and minimum levels of charge in the battery. Achieving 2000 cycles with NiMH batteries requires they only get charged up to 90% capacity and discharged to 10%. So for normal operation 20% of the capacity is reserved.