Home notebook smart battery Maintenance
Aspeaker at a battery seminar remarked that, “The battery is a wild animal and artificial intelligence domesticates it.” An ordinary or ‘dumb’ battery has the inherit problem of not being able to display the amount of reserve energy it holds. Neither weight, color, nor size provides any indication of the battery’s state-of-charge (SoC) and state-of-health (SoH). The user is at the mercy of the battery when pulling a freshly charged battery from the charger.
Help is at hand. An increasing number of today’s rechargeable batteries are made ‘smart’. Equipped with a microchip, these batteries are able to communicate with the charger and user alike to provide statistical information. Typical applications for ‘smart’ batteries are notebook computers and video cameras. Increasingly, these batteries are also used in advanced biomedical devices and defense applications.
There are several types of ‘smart’ batteries, each offering different complexities, performance and cost. The most basic ‘smart’ battery may only contain a chip to identify its chemistry and tell the charger which charge algorithm to apply. Other batteries claim to be smart simply because they provide protection from overcharging, under-discharging and short-circuiting. In the eyes of the Smart Battery System (SBS) forum, these batteries cannot be called ‘smart’.
What then makes a battery ‘smart’? Definitions still vary among organizations and manufacturers. The SBS forum states that a ‘smart’ battery must be able to provide SoC indications. Benchmarq was the first company to commercialize the concept of the battery fuel gauge technology. Early IC chips date back to 1990. Several manufacturers followed suit and produced ‘smart’ chips for batteries.
During the early nineties, numerous ‘smart’ battery architectures with a SoC read-out have emerged. They range from the single wire system, the two-wire system and the system management bus (SMBus). Most two-wire systems are based on the SMBus protocol. This book will address the single wire system and the SMBus.
The Single Wire Bus
The single wire system is the simpler of the two and does all the data communications through one wire. A battery equipped with the single wire system uses only three wires, the positive and negative battery terminals and the data terminal. For safety reasons, most battery manufacturers run a separate wire for temperature sensing. Figure 7-1 shows the layout of a single wire system.
The modern single wire system stores battery-specific data and tracks battery parameters, including temperature, voltage, current and remaining charge. Because of simplicity and relatively low hardware cost, the single wire enjoys a broad market acceptance for high-end mobile phones, two-way radios and camcorders.
Most single wire systems do not have a common form factor; neither do they lend themselves to standardized SoH measurements. This produces problems for a universal charger concept. The Benchmarq single wire solution, for example, cannot measure current directly; it must be extracted from a change in capacity over time.
In addition, the single wire bus allows battery SoH measurement only when the host is ‘married’ to a designated battery pack. Such a fixed host-battery relationship is feasible with notebook computers, mobile phones or video cameras, provided the appropriate OEM battery is used. Any discrepancy in the battery type from the original will make the system unreliable or will provide false readings.
Figure 7-1: Single wire system of a ‘smart’ battery.
Only one wire is needed for data communications. Rather than supplying the clock signal from the outside, the battery includes an embedded clock generator. For safety reasons, most battery manufacturers run a separate wire for temperature sensing.
14. Get yourself a more efficient notebook - notebooks are getting more and more efficient in nature to the point where some manufacturers are talking about all day long batteries. Picking up a newer more efficient notebook to replace an aging one is usually a quick fix.
15. Prevent the Memory Effect - If you’re using a very old notebook, you’ll want to prevent the ‘memory effect’ - Keep the battery healthy by fully charging and then fully discharging it at least once every two to three weeks. Exceptions to the rule are Li-Ion batteries (which most notebooks have) which do not suffer from the memory effect.
Bonus Tip #1: Turn off the autosave function. MS-Word’s and Excel’s autosave functions are great but because they keep saving regular intervals, they work your hard driver harder than it may have to. If you plan to do this, you may want to turn it back on as the battery runs low. While it saves battery life in the beginning, you will want to make sure your work is saved when your battery dies.
Bonus Tip #2: Lower the graphics use. You can do this by changing the screen resolution and shutting off fancy graphic drivers. Graphics cards use as much or more power today as hard disks - Thanks Andrew
Update 7/7/07: Bonus Tip #1 to give caution about turning off autosave, tip #8 to change information about discharging batteries - thanks to all who pointed it out. Added Bonus tip #2, Tip #1 to add in clause in regards to Mac OSX, Tip #1 about the spinning of hard drives - thanks to all who pointed it out.
Downtime almost always occurs at critical moments. This is especially true in the public safety sector where portable equipment runs as part of a fleet operation and the battery is charged in a pool setting, often with minimal care and attention. Under normal conditions, the battery will hold enough power to last the day. During heavy activities and longer than expected duties, a marginal battery cannot provide the extra power needed and the equipment fails.
Rechargeable batteries are known to cause more concern, grief and frustration than any other part of a portable device. Given its relatively short life span, the battery is the most expensive and least reliable component of a portable device.
In many ways, a rechargeable battery exhibits human-like characteristics: it needs good nutrition, it prefers moderate room temperature and, in the case of the nickel-based system, requires regular exercise to prevent the phenomenon called ‘memory’. Each battery seems to develop a unique personality of its own.
Memory: myth or fact?
The word ‘memory’ was originally derived from ‘cyclic memory’, meaning that a NiCd battery can remember how much discharge was required on previous discharges. Improvements in battery technology have virtually eliminated this phenomenon. Tests performed at a Black & Decker lab, for example, showed that the effects of cyclic memory on the modern NiCd were so small that they could only be detected with sensitive instruments. After the same battery was discharged for different lengths of time, the cyclic memory phenomenon could no longer be noticed.
The problem with the nickel-based battery is not the cyclic memory but the effects of crystalline formation. There are other factors involved that cause degeneration of a battery. For clarity and simplicity, we use the word ‘memory’ to address capacity loss on nickel-based batteries that are reversible.
The active cadmium material of a NiCd battery is present in finely divided crystals. In a good cell, these crystals remain small, obtaining maximum surface area. When the memory phenomenon occurs, the crystals grow and drastically reduce the surface area. The result is a voltage depression, which leads to a loss of capacity. In advanced stages, the sharp edges of the crystals may grow through the separator, causing high self-discharge or an electrical short.
Another form of memory that occurs on some NiCd cells is the formation of an inter-metallic compound of nickel and cadmium, which ties up some of the needed cadmium and creates extra resistance in the cell. Reconditioning by deep discharge helps to break up this compound and reverses the capacity loss.
The memory phenomenon can be explained in layman’s terms as expressed by Duracell: “The voltage drop occurs because only a portion of the active materials in the cells is discharged and recharged during shallow or partial discharging. The active materials that have not been cycled change in physical characteristics and increase in resistance. Subsequent full discharge/charge cycling will restore the active materials to their original state.”
When NiMH was first introduced there was much publicity about its memory-free status. Today, it is known that this chemistry also suffers from memory but to a lesser extent than the NiCd. The positive nickel plate, a metal that is shared by both chemistries, is responsible for the crystalline formation.
New NiCd cell.
The anode is in fresh condition (capacity of 8.1Ah). Hexagonal cadmium hydroxide crystals are about 1 micron in cross section, exposing large surface area to the liquid electrolyte for maximum performance.
Cell with crystalline formation.
Crystals have grown to an enormous 50 to 100 microns in cross section, concealing large portions of the active material from the electrolyte (capacity of 6.5Ah). Jagged edges and sharp corners may pierce the separator, which can lead to increased self-discharge or electrical short.
Restored cell.
After pulsed charge, the crystals are reduced to 3 to 5 microns, an almost 100% restoration (capacity of 8.0A). Exercise or recondition are needed if the pulse charge alone is not effective.
Figure 10-1: Crystalline formation on NiCd cell.
Illustration courtesy of the US Army Electronics Command in Fort Monmouth, NJ, USA.
In addition to the crystal-forming activity on the positive plate, the NiCd also develops crystals on the negative cadmium plate. Because both plates are affected by crystalline formation, the NiCd requires more frequent discharge cycles than the NiMH. This is a non-scientific explanation of why the NiCd is more prone to memory than the NiMH.
The stages of crystalline formation of a NiCd battery are illustrated in Figure 10-1. The enlargements show the negative cadmium plate in normal crystal structure of a new cell, crystalline formation after use (or abuse) and restoration.
Lithium and lead-based batteries are not affected by memory, but these chemistries have their own peculiarities. Current inhibiting pacifier layers affect both batteries — plate oxidation on the lithium and sulfation and corrosion on the lead acid systems. These degenerative effects are non-correctible on the lithium-based system and only partially reversible on the lead acid