Juicing Up Your Gadget Battery Power
There are proper charge rates and maximum safe discharge rates that you need to know about if you go the do-it-yourself route -- you can cause explosions. The best sources of information on this subject are those related to model airplanes. Model aircraft hobbyists have had battery weight and size issues for a lot longer than us gadget users, and have been early adopters of lithium polymer.
08/02/12 5:00 AM PT
I've written about keeping your devices powered while on the road before, and looked at techniques to reduce draw -- like reducing screen brightness and switching off phone radios. I also took a broad-brush look at different technologies, like battery packs and solar, in the same piece.
Now I'm going to explain how to choose the right rechargeable battery, called a "secondary cell"; and choose the right technology, like solar, to increase your time between battery charges.
Lithium Polymer vs. Lithium Ion
Stock, extended and additional battery packs for gadgets currently use lithium technology. This chemistry has replaced nickel cadmium and nickel metal hydride rechargeable batteries that were prone to memory effect.
Choose polymer over ion when it's offered. Lithium polymer, or Li-Po, is better for gadget purposes because it's lighter. It also can be manufactured in varied shapes, unlike lithium ion, leading to smaller form-factors. Li-Po is more expensive though.
There are three types of solar panel. Each offers different levels of efficiency:
- Monocrystaline, the more expensive technology, provides the best power-to-size ratio;
- Monocrystaline along with polycrystalline also has good longevity;
- Amorphous is used where there aren't space constraints.
Choose monocrystaline technology when offered for gadgets.
Calculating NeedsThis is a crucial step, because it allows you to thwart dubious marketers trying to sell you inappropriate battery packs and solar panels.
It's also important because as battery technology becomes more efficient, size and weight are not accurate indicators. Heft has become irrelevant.
Step 1: Identify Requirements
Open the case of your device and retrieve the battery to learn the battery capacity. Look for the amperage specifications printed on the battery, for example "1200 mAh," on a Samsung phone. If the battery isn't removable, perform a Web-based product search.
Identify how many volts the device uses. Anything that's powered by USB is 5 volts.
Read the specifications on the charger. Use the supplied OEM device charger to obtain the existing power specifications, and consequently the requirements of any replacement power source.
For example, laptops can require 19.5 volts and 3.34 amps; Smartphones can require 5 volts and 1 amp.
The stock 1200-mAh battery used in the example needs a replacement battery of at least that specification to perform the same as stock, but it can be of greater specification.
Step 2: Understand a Few Basic Concepts
Rechargeable battery capacity, for our purposes, is measured in milliamp hours (mAh). This is a measure of the amount of energy that the battery can hold. The "hour" refers to the amount of energy that can be drawn over a one-hour period.
Older battery technologies like Lead Acid often use amp hour (Ah) as a measurement. It's the same concept: One milliamp hour is the same as one amp hour.
For example, an 18,000-mAh Li-Po battery that you'd see in a battery pack measures the same in energy as an 18-Ah Lead Acid battery that you'd see operating a wheelchair motor.
The battery theoretically provides 18 amps over a one-hour period before it becomes exhausted. Alternatively, it would theoretically provide 1 amp over an 18-hour period.
I recently used an 8.000-mAh battery to operate a 1-amp cable modem for 7.5 hours.
Think of the amp is the unit of electrical flow. Volts are a measurement of the force.
Step 3: Eliminate Batteries and Technology Choices That Won't Work
Verify the voltage on the new battery source. A 12-volt 18-amp Lead Acid battery at 30 bucks, while cheap and full of power, won't charge a laptop at 19 volts without an inverter, or a way to step up the voltage.
Output voltage on the battery pack should match input voltage on the device. However, output amps on the battery pack can be greater than the input amps required (obtained from the OEM power supply label) by the device -- but not less. The device will draw what it needs.
Solar vs. Battery
Solar panel output is measured in watts rather than milliamp hours used for storage like batteries. Common US$80 gadget-oriented solar panels supply 7 watts in full sun.
The watts your device needs to work is calculated by multiplying volts by amps.
For example, a Dell laptop power supply that's 19.5 volts and draws 3.34 amps equates to 65.13 watts for the Dell. The 7-watt solar panel isn't going to charge or operate the Dell.
However, if the device's force (voltage) required was 5 volts, and the electrical flow (amps) was 1 amp, and multiplying them makes 5 watts, the device -- like a smartphone -- would charge. The solar panel specifications would be adequate.
Budget vs. Weight Issues
The Li-Po battery pack from the earlier example, including its 5-volt and 19-volt ports, weighs in at 8 oz. and is 7 x 3 x 1 inches. The Lead Acid battery from the earlier step, on the other hand, weighs 13 lbs. and has dimensions of about 7 x 6.5 x 3 inches.
The Lead Acid battery costs $30 and the Li-Po comes in at $150.
Step 4: Other Considerations
Read the labeling on the battery pack you're buying. If the Dell laptop power supply requires 19.5 volts and 3.34 amps, make sure the output capacity of the battery pack port is sufficient.
Look for "Output 19.5v, 3500 mAh" or similar on the new battery pack. Again, work off the existing power supply here, not the existing battery. In this example, the output is sufficient.
Step 5: Become a Battery Geek
Buy a LiPo battery "pack" -- that's a configured set of batteries complete with case and ports -- rather than a bunch of individual 3.7-volt Li-Po battery cells unless you want to become a battery geek.
There are proper charge rates and maximum safe discharge rates that you need to know about if you go the do-it-yourself route -- you can cause explosions.
The best sources of information on this subject, if you want to explore it, are those related to model airplanes. Model aircraft hobbyists have had battery weight and size issues for a lot longer than us gadget users, and have been early adopters of lithium polymer.
Warning: Never mix types or batches of lithium battery. It's unsafe.
Want to Ask a Tech Question?
Is there a piece of tech you'd like to know how to operate properly? Is there a gadget that's got you confounded? Please send your tech questions to me, and I'll try to answer as many as possible in this column.
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