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Wednesday, April 2, 2014

Product review: Pawtec Dual 2-Port USB Wall Charger 5V 4.2A


Pawtec wall charger is a compact 2 port charger with retractable prongs. Due to its nice size it takes up just one slot on a power strip. It is 2"L x 2"W x 1"H and weighs 2.8 oz. The package includes a travel pouch.

I tested Pawtec charger with Samsung Nexus phone and iPad Mini tablet.

I run the same set on tests on each battery pack I own, so I can compare them to each other using "apples to apples" comparison. This set of tests allows me to compare different chargers as well as see how performance changes with each upgrade of the operating system. I am including the details of the tests below for those who want to see the nitty gritty.

For those who are interested in the bottom line this battery pack worked consistently with both devices and charged the devices charging them at slightly below average rate.

★ To prolong battery life

Li-ion batteries do not need to be fully charged nor is it desirable to do so. In fact, it is better not to fully charge, because high voltages stresses the battery. Li-ion should never be discharged too low. This is why battery manufacturers typically ship batteries with a 40 percent charge. The low charge state reduces aging-related stress while allowing some self-discharge during storage. If you plan to store the battery without using it apply a partial charge before a long storage period.

★ How I tested this battery pack

I use a USB current monitor and a charging test to test each port. The current monitor shows the voltage and the current flowing between the battery and the device.

I started running these tests when my Android devices had HoneyComb operating system so I was able to observe the improvements in charging with different version of the Android OS. Before 4.21 I could only get fast charging on 1A port, and would get bad performance on 2.1A port on my Android devices. After upgrade to Jelly Bean 4.21 I see the same performance on 2A and 1A ports as it is controlled by the device negotiating the protocol with the charger. Google reverse engineered the Apple protocol and now my Android devices typically charge similar in speed on both ports of a good charger. This is not true for Apple devices. They do better on ports designed for Apple (2.1A ports).

An addition variable for Android devices is whether a data cable or charging cable is used to charge the device. The charging cables short the two data connections together (rendering them useless for data transfer), but this fools devices to see the cable as an AC power connection, and thus accept the higher current of the charging source.

The 10 minutes test consists of charging each mobile device on each port of the battery pack for 10 minutes and measure how much each unit was charge in that 10 minute period. Since the charging speed is non-linear I start charging each device from approximately the same charge level. I use Battery App by Elvison to determine how each device recognized the charging source. 'AC' status means the charging is at full charging rate. 'USB' status indicates charging at a lower charging rate. 'Discharging' status means that the charging rate is below the power that the device is consuming so it slows down the discharge rate but does not re-charge.

★ Test Results:

✔ Samsung Galaxy Nexus Phone
Port 1: AC charging rate ----- 4% change in charge in 10 minutes
Port 1: current monitor: ~~~~~ 0.95A and 5.12V

Port 2: AC charging rate ----- 4% change in charge in 10 minutes
Port 2: current monitor: ~~~~~ 0.96A and 5.12V

✔ iPad Mini Tablet
Port 1: AC charging rate ----- 1% change in charge in 10 minutes
Port 1: current monitor: ~~~~~ 1.46A and 5.10V

Port 2: AC charging rate ----- 3% change in charge in 10 minutes
Port 2: current monitor: ~~~~~ 1.53A and 5.12V

★ Summary
This is a small 2 port charger. It takes up just one slot on the old fashioned power strip, and since I am always running out of space on my power strips this is a big plus for this charger.

You can find it on Amazon by following this link.

Ali Julia review ★★★★☆

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