Laptop Batteries Repairs / Replacement

The Battery storage capacity is the amount of energy the battery can store to power a portable device such as a notebook computer. The lower the storage capacity of a battery, the shorter amount of time it can power a portable device. All rechargeable batteries gradually lose their storage capacity. This loss in storage capacity (aging) is irreversible and cannot be restored. The maximum storage capacity of a new battery can be very different from the maximum storage capacity of a battery after one year of use.
If the system detects that the storage capacity of the battery is very low, it will display an alert:.

  The system has detected the storage capacity of the battery stated below to be very low.
  For optimal performance, this battery may need to be replaced.
  Primary (internal) Battery (601)

Differences between primary and secondary battery messages

If Primary (internal) Battery (601) appears in the alert message, it means the measured storage capacity of the primary (internal) battery is less than 25% of the original storage capacity. The number “601” denotes the associated error code that is recorded in the system log.

If Secondary (external) Battery (602) appears in the alert message, it means the measured storage capacity of the secondary (external) battery is less than 25% of the original storage capacity. The number “602” denotes the associated error code that is recorded in the system log.

Most laptop batteries are smart. This means that the pack consists of two parts: the chemical cells and the digital circuit. If the cells are weak, cell replacement makes economic sense. While nickel-based cells are readily available, lithium-ion cells are commonly not sold over the counter, and most manufacturers only offer them to authorized pack assemblers. This precaution is understandable given liability issues. Read also about Safety Concerns and Protection Circuits. Always use the same chemistry; the mAh rating can vary if all cells are replaced.

A laptop battery may have only one weak cell, and the success rate of replacing the affected cell depends on the matching with the others. All cells in a pack must have a similar capacity because an imbalance shortens the life of the pack. Read more about Can Batteries Be Restored?. Furthermore, the state-of-charge of all cells being charged for the first time should have a similar charge level, and the open-circuit voltages should be within 10 percent of each other. Welding the cells is the only reliable way to get dependable connection. Limit the heat transfer to the cells during welding to prevent excess heat buildup.

The typical SMBus battery has five or more battery connections consisting of positive and negative battery terminals, thermistor, clock and data. The connections are often unmarked; however, the positive and negative are commonly located at the outer edges of the connector and the inner contacts accommodate the clock and data. (The one-wire system combines clock and data.) For safety reasons, a separate thermistor wire is brought to the outside.

Terminal connection of a typical laptop battery

The positive and negative terminals are usually placed on the outside; no norm exists on the arrangement of the other contacts.

Some batteries are equipped with a solid-state switch that is normally in the “off” position and no voltage is present on the battery terminals; connecting the switch terminal to ground often turns the battery on. If this does not work, the pack may need a proprietary code for activation, and battery manufacturers keep these codes a well-guarded secret.

In some cases the chemical battery can be restored, but the fuel gauge might not work, is inaccurate, or will provide wrong information. After repackaging, the battery may need some sort of initialization/ calibration process. Simply charging and discharging the pack to reset the flags might do the trick. A “flag” is a measuring point to mark and record an event.

The circuits of some smart batteries must be kept alive during cell replacement. Disconnecting the voltage for only a fraction of a second can erase vital data in the memory. The lost data could contain the resistor value of the digitized shunt that is responsible for the coulomb counter. Some integrated circuits (IC) responsible for fuel gauge function have wires going to each cell, and the sequence of assembly must to be done in the correct order.

To assure continued operation when changing the cells, supply a secondary voltage through a 100-Ohm resistor to the circuit before disconnection and remove the supply only after the circuit receives voltage again from the new cells. Cell replacement of a smart battery has a parallel with open-heart surgery, where doctors must keep all organs of the patient alive.

Anyone repairing an SMBus battery needs to be aware of compliance issues. Unlike other tightly regulated standards, the SMBus allows some variations, and this can cause problems when matching battery packs with existing chargers. The repaired SMBus battery should be checked for compatibility before use.

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