Some basic rules must be followed in repairing a ‘smart’ battery. If the cells are weak, cell replacement makes economic sense. While Nickel-based cells are readily available, Lithium-ion cells are not sold on the open market. Most manufactures offer them only in a completed battery pack(thinkpad x41 battery,thinkpad x40 battery), together with protection circuit. This precaution is understandable when considering the danger of explosion and fire if the cells are assembled in a careless way. Always replace the pack with the same chemistry cells.

During cell replacement, the circuit of many ‘smart’ batteries must be kept alive with a supply voltage. Disconnecting the circuit, if only for a fraction of a second, can erase vital data and render the circuit unusable. To assure continued operation when changing the cells, connect a secondary voltage through a 100 Ohm resistor before disconnecting the thinkpad x40 battery cells. Remove the secondary supply only after the circuit is fed with the needed operating voltage from the new cells.

The open terminal voltages of the replacement cells should be within 10% of each other. Welding the lenovo thinkpad x40 battery cells is the only reliable way to get dependable service. Attention must be paid in limiting the heat transferred to the cells during welding. Excess heat can damage the cells.

During storage, each cell has self-discharged to a different charge level. This is especially important on Nickel-metal-hydride. To assure proper charge of all cells without overcharging some, trickle charge the newly repaired pack for about 14 hours, then apply a charge, discharge and charge cycle. Such a cycle is also needed to reset the battery’s fuel gauge circuit. Lithium-ion can accept a normal charge lasting about 3 hours. The thinkpad x41 battery and thinkpad x40 battery analyzers feature a program that performs this priming function automatically.