Batteries – One Size Does Not Fit All

I have a Palm Zire 72 and a Palm m505 PDA. If I buy a Palm Zire 72 Battery that is 3.7 volts can I plug it into a Palm m505 and have that battery power both devices as needed?

In a nut shell the question above seeks to ascertain if all 3.7 volt batteries are the same?

The quick answer is no – all 3.7 volt batteries are “not” the same – and a battery specifically designed for a Palm Zire 72 will not be compatible with a Palm m505 PDA.

Let me explain.

It is true that all batteries share similar components and share common electrical measurements. But just because all batteries have some common components and measurements does not mean at all that you can interchange batteries with various devices even if the technical ratings are the same. Note that a component is something tangible and a measurement is intangible – a result of an action contained within the battery system.

Quick Review: What is a Battery and how does it work?

A battery in its most basic definition is a device that converts chemical energy into electrical energy. Batteries have two electrodes, an anode (the negative end) and a cathode (the positive end). Collectively the anode and the cathode are called the electrodes. What is positve and what is the negative terminal? It would be great to simply say that the anode is negative and the cathode is positive, however, that is not always the case. Somtimes the opposite is true depending on battery technology.

In between the battery’s two electrodes runs an electrical current caused primarily from a voltage differential between the anode and cathode. The voltage runs through a chemical called an electrolyte (which can be either liquid or solid). This battery consisting of two electrodes is called a voltaic cell.

Electrical measurements that can be gleaned from battery operations inclued the measurements of:

Volts – or V – is the electrical measure of battery’s energy potential. For example you can think of energy potential as the pressure being exerted by all the electrons of a PDA Battery’s negative terminal as they try to move to the positive terminal.

Amps – or A – which is a measure of the volume of electrons passing through a wire in a one second. One Amp equals 6.25 x 1018 electrons per second.

Watts: Volts x Amps = Watts. Watts are important because a watt represents the electrical energy spent by a battery (power generator) and used by an electrical device. Watts in effect is the measure of the amount of work done by certain amperage (amount) of electric current at a certain pressure or voltage.

Now beyond that basic review of the common components and measurements of batteries begins the radical differences between batteries. If you have a PDA, MP3, MP4, Laptop, Cell Phone, Smartphone, DVD players, or other electronic devices then more likely then not the battery within your device is a high capacity smart battery pack.

What is a high capacity smart battery pack? A high capacity smart battery pack is a complex battery system designed to power high tech electronic devices.

To construct a smart battery the battery manufacturer must carefully plan the internal battery design environment by considering the:

• design parameters
• current requirements
• capacity and runtime requirements
• temperature requirements
• safety requirements
• ambient operational/non-operational temperatures

As a design for a smart battery pack is considered manufacturers must evaluate the differences in components in relation to their design environment. Proper component evaluation and specification selection based on the intended application will determine the ultimate performance of the entire battery.

To give you an example of why smart batteries are carefully designed consider a PDA that when turned on explodes (don’t think it can’t happen) thankfully it occurs very rarely. To be a more reassuring the US Consumer Product Safety Commission has noted that 339 battery-related overheating incidents have occurred since 2003. Since conservative estimates puts the sale and use of devices containing smart batteries in excess of 100 million battery related devices during the same period makes the 339 incidents reported by the Saftey Commission at .000003% (a very small percent) of all battery related devices on the market. What is preventing more battery related fires -reliable and safe design under worst-case conditions is especially critical when designing with lithium based batteries. Specifically over-voltage and under-voltage of the cells and over-current of the battery pack.

Now with all this said I can tell you again, almost emphatically, that not all batteries are the same. From battery to battery the internal design will be different depending on the device the battery was specifically built to work within.

Until next time, Dan Hagopian –
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