In my previous installment of Understanding Battery Life we reviewed what battery life means; how battery life is measured; what factors determine and impact battery life; and finally when do batteries begin to lose life. In part 2 of Understanding Battery Life we will look at a battery’s internal design. A battery design is an important foundation on understanding battery life because of the fact that a battery is a consumable product (a batteries internal chemical is consumed upon activation) and that this consumption shortens the batteries life over time. Therefore to know what the maximum potential of a battery is (the starting point) before the battery is ever consumed is good because once a battery is used even once a battery begins a gradual degradation to the point of no longer being able to power a device (typically about 80% of the batteries capacity – less than 80% capacity is often times too low for a device to recognize the battery).
Initial Technical Ratings
The initial technical ratings of a battery are the specs (the technology) that define the battery. They are represented in most battery websites as the voltage, mAh (battery amperage/capacity), and battery chemistry. There is much that can be written, and has been written, about each of these factors individually; however, what is key to know about the battery’s technical specs is that they were all decided upon prior to the production of the battery and predestined to operate at specific power levels. Knowing this allows the buyer and seller of a battery to understand in advance how the battery will perform, thus disclosing upfront the capability of the battery.
A battery’s design is a compilation of several required parameters.
- Battery Voltage
- Battery Current
- Battery Capacity
- Battery Chemistry
- Battery Temperature
- Battery Protection Circuitry
- Battery Smart Technology
Before we begin I want to note that Battery Protection Circuitry and Battery Smart Technology require minimal battery usage and although critical components of battery design it is not germane to battery life in great quantity and therefore will not be discussed in this article. I do have more info available on my blog which can be accessed from the links at the end of this article.
Critical to battery design is to know how much voltage is required? Voltage is the electrical measure of energy. To know the voltage requirements we need to know the upper and lower voltage range (nominal range).
The second critical key component to battery design is the battery’s current requirements. PDAs, MP3s and other portable devices, for the most part, utilize a constant power discharge to operate. This means that the amount of current will increase as the battery discharges electricity in order to maintain constant power. So we will need to ultimately know the maximum current required. This is important since knowing the max current requirement will influence the necessary protection of chemistry, circuitry, wire, and capacity amongst others. Again we must know the current requirement over the entire nominal voltage range of the battery including start-up currents, surges (intermittent transient pulses). One other important aspect to know about current requirements is the inert current drain of the device. Devices, even when powered down, require small amounts of current to power memory, switches and component leakage.
The third key component to know of internal battery design is the necessary battery capacity and runtime. This will define the overall physical size of the battery. Capacity and runtime is measured in Amperes.
When we consider the design capacity we must determine the chemical needed to insure that the necessary runtime will be met. Lithium is used because of its electrochemical properties. Lithium is part of the alkali family of metals a group of highly reactive metals. Lithium reacts steadily with water. In addition the per unit volume of lithium packs the greatest energy density and weight available for this grouping of reactive metals.
Ambient operational temperatures are also important because the internal heat of the battery compartment will dramatically affect the life of a battery. Usage and storage patterns are external effect that will also affect battery life and are the responsibility of a user (for example do not leave your device in a hot car with the windows rolled up, or take your device into a sauna).
In my next segment on Understanding Battery Life we will look at two other aspects of battery life and that is how individual usage and internal technical factors affect battery life.
Until next time – Dan Hagopian, www.batteryship.com
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