What’s Inside a Laptop Battery Pack?

Have you ever what secrets lie in a laptop battery pack? My Thinkpad X60 battery used to hold about 4 hours before but now the lenovo laptop battery can only hold about 1 hour after using for 3 years. Can I replace the cells inside?

Well, open the casing, here is the anatomy of a Li-Ion notebook battery:

A. Temperature sensors

If the temperature reaches a high level for whatever reason, the electronics cut off the current to isolate the batteries from charging or discharging to avoid overheating. There might be temperature sensors in the battery compartment, feeding its own safety systems.

B. Lithium ion cell

6 cell or more AA Li-Ion cell are wired together within a typical battery pack. Cell Sensor Wire is routed between cells and cells are insulated with special insulating paper.

C. Voltage regulator circuit

This regulates the voltage supplied by the battery during charging and discharging to ensure consistent current. Therefore, make sure the voltage is correct before buying a replacement battery is always important.

D. Notebook connector

This is shrouded and designed to minimise the risk of short circuits when the battery pack is separate from the main equipment. Even if the plastic shroud is damaged, the circuitry inside the pack should detect short circuit conditions and protect the cells from rapid discharge.

E. Voltage tap

Most consumer equipment treats a stack of cells as a single battery, but this can be dangerous in lithium ion. As the cells age, some will lose capacity faster than others — and if one cell becomes flat before the others, it can actually start to charge in reverse, which is a highly dangerous condition. The internal circuitry of the battery pack thus has to monitor cells separately and shut down the whole pack if one cell is too far out of balance.

F. Battery charge state monitor

Many lithium ion packs have a built-in meter consisting of a row of LEDs and a button. To check battery charge, press the button and the number of LED lights that appear will tell you charge status. If all lights appear, you have a fully charged battery. This can become more inaccurate over time; more modern cells will recalibrate themselves.

Anatomy of a Li-Ion notebook battery

Well, I think it’s better not putting new rechargeable AA batteries to replace the old ones by yourself otherwise you are taking risks of explosion or laptop fire since there are further more controls and insulation needed inside.

Related Reading: OEM or Aftermarket? Laptop Battery Comparison