Laptop batteries differ from other types of batteries in that they provide a relatively short service life and are expensive to replace. In this article we look at the reasons why these batteries do not last and examine the high replacement cost. We also look into the possibilities of repairing them.
Most of today’s laptop computers are powered with Lithium-ion batteries.(thinkpad t61 battery,thinkpad t40 battery)
Under good conditions, Lithium?ion provides 300 to 500 discharge/charge cycles or 2 to 3 years of service from the time the thinkpad t40 battery leaves the production line. The capacity loss occurs through increased internal resistance caused by cell oxidation. Eventually the resistance reaches a point where the battery can no longer deliver the needed energy although the energy may still be present in the battery. There are no remedies to restore the capacity when worn out. Heating the battery will momentarily improve the performance.
Figure 1: illustrates the recoverable capacity at various storage temperatures and charge levels over one year. Nickel-based chemistries, a chemistry that is also used in laptops, is illustrated on the right column. The capacity loss progresses on a quasi linear scale for the second and third year.
During use, the battery compartment in many laptops rises to about 45°C (113°F). The combination of high charge level and elevated ambient temperature presents an unfavorable condition for the battery. This explains the rather short lifespan of lenovo batteries.
The thinkpad T42 battery is ’smart’, meaning that some form of communications occurs between the battery and user. The definition of ’smart’ varies among manufacturers and regulatory authorities. Some manufacturers call their batteries ’smart’ by simply adding a chip that sets the charger to the correct charge algorithm. The Smart Battery System (SBS) forum states that a ’smart’ battery must provide state-of-charge (SoC) indications.
There are two common architectures of ’smart’ batteries. They consist of the single wire system found on high-end radio communications devices and video camera equipment, and the two-wire system, typically used on laptops. The two-wire system is usually configured as System Management Bus. Because of its common use in laptops, we will focus on the system. Figure 2 shows the layout.
Figure 2: Two-wire system.
The is based on a two-wire system using a standardized communications protocol. This system lends itself to standardized state-of-charge and state-of-health measurements.
The battery has five or more thinkpad t61 battery connections consisting of the positive and negative battery terminals, thermistor, clock and data. The connections are commonly not marked and attempting to test this type of battery appears complicated. Figure 3 describes the functions of a battery with 6 connections.
Figure 3: Connections of a typical laptop battery. The positive and negative terminals are usually placed on the outside; no norm exists on the arrangements of the contacts.
The positive and negative battery terminals are commonly located at the outer edges of the connector. The inner contacts accommodate the clock and data. (On a one-wire system, clock and date is combined.) For safety reasons, a separate thermistor wire is brought to the outside. This allows temperature protection if the digital communication is disabled.
Some batteries are equipped with a solid-state switch that is normally in the off position. In such as case, no voltage is present. Connecting the switch control terminal to ground will turn the thinkpad X60 battery on. If this does not work, a proprietary code may be needed to activate the battery.
Once the connection to the battery terminals is established, charging should be possible. If the charge current stops after 30 seconds, a digital code may be required. Some battery manufacturers go as far as to add a defined end-of-life switch. If a preset age, cycle count or capacity is surpassed, the battery stops functioning. When asking why such codes are added, the manufacturers explain that enduring safety can only be guaranteed if the battery is tamper-free and well performing. This makes common sense but the leading motive may be pricing. In the absence of competition, replacement batteries can be sold at a premium price. Newer batteries(Lenovo N100 battery,lenovo N200 battery) are generally more service friendly than older ones.
It is recommended to utilize the thermistor during charge and discharge to protect the battery against over heating. The thermistor can be measured with the Ohmmeter. The most common thermistors are the 10 Kilo Ohm NTC type, which read 10kOhm at 20°C (68°F). NTC stands for negative temperature coefficient, meaning that the resister decreases with rising temperature. A positive temperature coefficient (PCT) will increase the resistance. Warming the battery with your hand may be sufficient to detect a change in resistor value.
Figure 4: The Cadex SM2+ charger This level-3 charger serves as charger, conditioner and quality control system. The charger reads the battery’s state-of-health and flags those that fall below the set target capacity. Each bay operates independently and charges Nickel-cadmium, Nickel-metal-hydride and Lithium?ion chemistries in approximately three hours. ‘Dumb’ batteries can also be charged but no SoH information is available.
For full battery service, a battery analyzer is recommended. The lenovo thinkpad t61 battery is a programmable battery analyzer capable of rapid testing, charging, priming and reconditioning a large variety of batteries. The battery packs connects by custom SnapLock battery adapters, programmable cables or the Cadex FlexArm adapter. The analyzer does not check the .
Figure 5: lenovo battery analyzer
The programmable lenovo services lithium, nickel and lead-based batteries. SnapLock battery adapters simplify the interface with different battery types. A quick test program measures battery state-of-health in 3 minutes, independent of charge. Nickel-based batteries are automatically restored if the capacity falls below the user-defined target capacity.
Summary
Laptop batteries can be repaired but such work only makes economical sense for smaller operators. The success rate varies with battery type. One must remember that the ’smart’ battery consists of two parts, the chemical cells and the digital circuit. In some cases, the chemical part can be fully restored but the fuel gauge may become inaccurate or other data may get corrupted.
Anyone attempting to repair battery must be aware of some non-compliance in the SBS forum. Unlike other tightly regulated standards, the protocol allows some variations. This may cause problems with existing chargers and the thinkpad T40 battery should be checked for compatibility before use. The need to test and approve the marriage between a specific battery and charger is unfortunate, given the fact that the battery is being promoted as being universal. Ironically, by adding more features to the charger and the battery, the higher are the likelihood of incompatibilities.