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By Chris De Herrera 
Copyright 1998-2007
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Battery FAQ
By Chris De Herrera, Copyright 1998, 2002
 Version 1.06  Revised 10/25/98

Introduction

As a user of portable technology you are a captive of your battery life. Each manufacturer has made decisions about the specific batteries supported. Others will work as well and some will work better than others.

Before we get started, the reader needs to know what volts and amperes are.  An analogy is Volts are like how fast the water is flowing on a river while amperes are how high the water is relative to the banks.  Just like water, electricity use will vary greatly based on conditions that can not be predicted with 100% accuracy.

Battery Types

There are the following different types of batteries that are available:

Battery Chemistry Description Company Size (AA size where possible) Milliampere Hours (mAh) Initial Voltage Device ending voltage Difference Self Discharge Rate Rechargeable Number of Recharges

(Cycles)

Alkaline Duracell, Energizer are the 2 leaders. AA 2000 1.5 .9 .6   No N/A
Lead Acid Portable Energy Products. Fully sealed. flat external proprietary packs 1800 to 5000 2.2 .9 1.3 3% per month Yes 500-2200 (PwrPlant 2000 mA)
Lithium Ion High density power (normally equivalent to 2 cells) cylindrical  proprietary packs 750 to ? 3.6 1.8 1.8 8% per month Requires special charging circuitry to avoid overcharging 500-1000
Lithium Polymer High density power (normally equivalent to 2 cells) Can be made into any format   3.6 1.8 1.8   Requires special charging circuitry to avoid overcharging 500-1000
Lithium Secondary Eveready AA 3000 1.6 .9 .7   No N/A
Nickel Cadmium Commonly known as NiCads AA 450 to 900 1.25 .9 .35 15% per month Yes 500-2200
Nickel Metal Hydride Commonly known as NiMH, KiwiGreen AA 1100 to 1500 1.2 .9 .3 30% per month Yes 500 (KiwiGreen  version 1 - 3800 mA version 2 - 4200 mA)
Renewals Rayovac AA 1800 1.5 .9 .6   Yes 25
Zinc Air InstantPower - requires air to use block 3300 5.6 (4 1.4v cells) varies   3 charges. Power diminishes when exposed to air. No N/A

Notes:

The Difference between the initial voltage and the device ending voltage is the amount that the voltage can drop before the batteries are no longer able to power the device.  The voltage discharge curves for all of these batteries are not linear so it is very difficult to calculate accurate battery life due to the variance in the amount of current used in PDA/Pocket PCs (ie:  you can go from a couple of milliamperes to 100 for basic operations to over 700 ma for PC Card use.  Also, the higher the amperage draw the faster the voltage drops.  As the voltage drops even more milliamperes are required to operate the unit at the same constant voltage through the power converter.

The KiwiGreen battery requires a special charger which is included.   The Pwrplant battery use the standard AC Adapter for your H/PC to charge the battery.

Battery Usage

Most users are using their batteries all the time in varying conditions.  The batteries start their day being used as little as a few milliamperes to power the memory so it won't be erased.  Most units can sit for days to months in this state without a problem.  When you turn your unit on the amount of current goes up to about 100 milliamperes (color units require a lot more due to the continuous use of the backlight).  With the backlight on the current goes up again to 400 milliamperes.  Now each unit has a power inverter to provide 3 volts to run the systems on.  The amount of milliamperes varies based on the input voltage. The lower the voltage, the more milliamperes required to generate a constant 3 volts out.  Color units require the backlight to be on constantly so you can see the screen. This means that they use even more power than the gray scale units and have shorter battery life.  The gray scale units have a reflective coating that allows the user to read them without the backlight on.  Color units can not be used with a reflective coating due to the thickness of the LCD display.

Now when you add a PC Card the unit has to do some magic!  As you can see the units are powered from 1.8 volts to about 3 volts.  Well PC Cards run on 5 volts.  In order to use these in your PDA/Handheld PC the power inverter is used to create 5 volts.  The amperage required to do this is up to 2 1/2 times the amount used at 3 volts (The lower the voltage of the batteries the more milliamperes required).  On top of that you lose up to 20% during the conversion.  So a PC Card modem that is rated at 200 milliamperes is actually requiring 600 milliamperes plus the 100 milliamperes to power the unit for a total of 700 milliamperes.  As you can see the PC Card power requirements should be monitored closely so that you can maximize your battery life.  ATA flash is rated at about 5 milliamperes in standby and about 50 to 100 for read and write so it is not as harsh on batteries as the modems are.

The good news is that Compact Flash cards use 3 volts to operate so they do not require higher voltage.  I recommend using Compact Flash for data storage and peripherals due to the lower voltage requirement.

Battery Care

The rule of thumb is to discharge your batteries fully then recharge each time.  Most users do not do this!  Instead they use their PDA/Handheld PC for a period of time less than a complete discharge and then charge it. This uses up the number of cycles that the battery can provide. The problem is that most devices do not fully discharge the batteries. Also, if you leave your unit plugged in there is a trickle charge going to the battery.  Over time this may reduce the battery life due to overcharging.  These units were not designed to be continuously charging for extended periods of time.

The NiCad and NiMH batteries are subject to what is commonly referred to as the memory effect.  Basically it is a change in the battery's ability to charge fully based on not being completely drained when it is charged.  The best solution is to periodically (perhaps monthly) fully discharge your batteries by running your unit until the unit will no longer turn on.  Then fully charge it. This cycle should be done at least twice in a row to keep the batteries in good condition.

The Lithium Ion and Lithium Polymer batteries are designed to be kept charged.  If the batteries are fully discharged they can reduce the number of charging cycles.  Further whey they fail, your PDA may not work at all.  I have seen this in notebook PCs as well.

Maximizing Battery Life

Here's a list of things you can do to maximize your battery life:

  1. Turn off the backlight when you do not need it.  Use a timer to turn it off automatically.

  2. Lower the volume of sounds. Turn off excess sounds you do not need like key clicks and screen taps.  Use shorter sounds when possible for notifications of events

  3. Turn your contrast to the minimum readable display.  The darker the contrast the more power required.

  4. Remove any PC Card or Compact Flash that is not in use.  Insert them only when needed.

  5. Reduce the amount of time before your PDA/Handheld PC goes to sleep.

  6. Minimize your use of IrDA (infrared) or Serial communications.  Both of these require more power.

For those of you using Windows CE, Sixxac PowerTime is available to assist you in keeping track of your battery life,  It is a battery monitoring tool that allows you to keep track of battery usage on Windows CE devices. It maintains information about current and past battery types, usage, estimated time left, and more. It's a great tool to help you decide on the best batteries for your usage patterns.

Conclusion

Based on this information, I hope you take better care of your batteries.  You depend on them for your ability to be mobile.  Don't forget to check with the manufacturer of your PDA/Handheld PC to see what type of battery they recommend.  Not all batteries will work well in all units!


If you find an error or can add to in the information provided above, feel free to e-mail me at [email protected] PC FAQ.

Related Links:

KiwiGreen Handheld PC Battery
Viatek Battery FAQ
Powerplant Handheld PC Battery

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