Laptop Batteries

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Contents

Types of Batteries

XO-1

In the XO-1 laptop, OLPC is using two battery chemistries 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.

XO-1.5 and XO-1.75

In the XO-1.5 and XO-1.75 laptops, OLPC solely uses the LiFePO4 battery technology, which is lighter and charges at higher temperatures.

XO-4

In the XO-4 laptop, OLPC worked to add back the option to use NiMH.

Vendors

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 See Special NiMH Charging System

GoldPeak LiFePO4

Typical capacity: 2900 mAh
Minimum capacity: 2800 mAh
Operating Voltage Range: 7.3V to 4V at 0.2C discharge current
Nominal Voltage 6.4V @ .2C
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%

GoldPeak BYD
NiMH LiFePO4
Typical capacity (mAh) 3050 2900 3150
Minimum capacity (mAh) 3000
Only 80% usable
2800 3100
Operating Voltage Range
@ 0.2C discharge current
7.5—5V 7.3—4V 7.5—5V
Operating Temp Charge 0 ~ +45°C 0 ~ +60°C -10 ~ +50°C
Operating Temp Discharge -20 ~ +50°C -20 ~ +70°C -20 ~ +55°C
Standard charge rate note CC-CV .1C CC-CV .8C up to 7.3V
Max charge rate 1.5C(4200 mA) 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 a 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.

See also

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