When trying to charge my android devices (Arc S and Nexus 7 (2013)), I noticed that when using new USB-cables, the charging process is going quite fast, but after some weeks (usually four-five) the charging process rapidly slows down, and some weeks later the devices don't charge anymore, i.e. resulting in the need of new cables. Is that a hardware failure, or why do I have to replace the cables every second to third month?
Hardware is not "capable" to decide charging rate based on "newness" or otherwise of cables
In all probability, USB cables you are using are of poor quality, wrong length and thickness
What I would suggest:
Why these specs for USB cable? Long explanation but needed to emphasize choosing the right USB cable
Ohm's Law Current = Voltage divided by Resistance
Resistance in turn depends on thickness
Resistance = Length divided by Area (ignoring resistivity)
Resistance is inversely proportional to the area of the wire
Less area = Thinner Wire = More Resistance = Less Current (you cannot make out thickness of the conductor by looking at it- they all seem to be equally thick but internally the conductor thickness varies)
Similarly, reducing length of wire decreases resistance
Arc S has 800 mA and Nexus 7 has 1150 mA Charging current rating and the cable should support that
Cable Length ,thickness, current rating required for device both matter when choosing the right cable. USB Cable Resistance: Why your phone/tablet might be charging slow relevant to your device specs says
For smartphones, with a requirement closer to 1A, 24AWG wires up to 2m could be sufficient, or 1m at 26AWG, and 50cm at 28AWG.
Nexus 7 is more choosy: It will stop charging if voltage levels drop and resistance comes into play again. Google Nexus 7 Charging goes into details and says
Nexus 7 will stop charging if the input voltage is less than the internal battery voltage plus 0.2 volts.
Repeating this test say once a month for a few months at least would give an indication if it is a hardware issue (weird as it sounds). If there isn't a significant change, it only confirms that poor USB cables being culprit
For everyone: USB Cable Resistance: Why your phone/tablet might be charging slow is a useful read to understand why it is a good idea to spend more but buy the right USB cable
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